feat: visual identity, theme toggle, custom CSS, loading states (M4)

Grounds the visual design in the product's own subject matter (vital-
signs monitoring) rather than generic dark-mode defaults: a signature
"pulse" green tied to healthy status (the accent color and the "up"
status color are the same hue - a steady green pulse reads as
healthy, same convention as a cardiac monitor), a small ECG-trace
brand mark, and a restrained pulsing-glow animation on healthy status
dots (prefers-reduced-motion respected) as the one deliberate motion
touch. Typography moves off the bare system-ui stack: IBM Plex Sans
for UI text, IBM Plex Mono with tabular numerals for metric values
(CPU/mem/uptime/latency), Space Grotesk used once for the wordmark -
chosen partly for IBM Plex's own systems-monitoring heritage.

Functional additions:
- Light/dark toggle, independent of config.yml's theme.mode, persisted
  to localStorage with a blocking inline script to avoid a flash of
  the wrong theme on load; auto mode now genuinely follows
  prefers-color-scheme instead of hardcoding dark.
- theme.customCssPath support via a new route handler that serves a
  user-mounted CSS file at runtime (can't be a build-time import,
  hence the targeted no-css-tags lint suppression), with a path-
  traversal guard since it's still reading from disk on every request.
- Loading-skeleton state for widgets awaiting their first WebSocket
  result, distinct from both the error state and genuine no-data.

Verified visually in Chrome: theme toggle switches instantly in both
directions, a live docker widget's status dot and monospace metrics
render correctly in both palettes, and config hot-reload still adds a
new widget without a page refresh.

components/widgets/Skeleton.tsx

@@ -0,0 +1,13 @@
+export function SkeletonLines({ count = 2 }: { count?: number }) {
+  return (
+    <div className="flex flex-col gap-1.5">
+      {Array.from({ length: count }, (_, index) => (
+        <div
+          key={index}
+          className="h-3 animate-pulse rounded bg-surface-raised"
+          style={{ width: `${70 - index * 15}%` }}
+        />
+      ))}
+    </div>
+  );
+}

components/widgets/StatusDot.tsx

@@ -14,12 +14,17 @@ function resolveColorClass(status?: Props["status"], health?: Props["health"]):
   return "bg-status-down";
 }
 
+function isHealthy(status?: Props["status"], health?: Props["health"]): boolean {
+  return status === "running" && health !== "unhealthy" && health !== "starting";
+}
+
 export function StatusDot({ status, health }: Props) {
   const label = status ? `${status}${health && health !== "none" ? ` (${health})` : ""}` : "unknown";
+  const pulse = isHealthy(status, health) ? "status-pulse" : "";
 
   return (
     <span
-      className={`h-2.5 w-2.5 shrink-0 rounded-full ${resolveColorClass(status, health)}`}
+      className={`h-2.5 w-2.5 shrink-0 rounded-full ${resolveColorClass(status, health)} ${pulse}`}
       title={label}
     />
   );

components/widgets/database/Widget.tsx

@@ -26,7 +26,9 @@ export function DatabaseWidget({ widget, widgetId }: { widget: DatabaseWidget; w
       <span className="text-xs text-fg-muted">{ENGINE_LABEL[widget.engine]}</span>
       {errorMessage && <span className="text-xs text-status-down">{errorMessage}</span>}
       {data?.uptimeSeconds != null && (
-        <span className="text-xs text-fg-muted">Uptime: {formatUptime(data.uptimeSeconds)}</span>
+        <span className="text-xs text-fg-muted">
+          Uptime: <span className="font-mono tabular-nums text-fg">{formatUptime(data.uptimeSeconds)}</span>
+        </span>
       )}
     </div>
   );

components/widgets/docker/Widget.tsx

@@ -3,6 +3,7 @@
 import type { Widget } from "@/lib/config/schema";
 import { useWidgetSubscription } from "@/lib/ws/client";
 import { StatusDot } from "@/components/widgets/StatusDot";
+import { SkeletonLines } from "@/components/widgets/Skeleton";
 import { formatBytes, formatUptime } from "@/lib/format";
 
 type DockerWidget = Extract<Widget, { type: "docker" }>;
@@ -30,17 +31,33 @@ export function DockerWidget({ widget, widgetId }: { widget: DockerWidget; widge
         <StatusDot status={data?.status} health={data?.health} />
       </div>
       {errorMessage && <span className="text-xs text-status-down">{errorMessage}</span>}
+      {!result && !errorMessage && <SkeletonLines />}
       {data && (
         <dl className="flex flex-col gap-1 text-xs text-fg-muted">
-          {data.uptimeSeconds !== null && <div>Uptime: {formatUptime(data.uptimeSeconds)}</div>}
-          {widget.showStats && data.cpuPercent !== null && <div>CPU: {data.cpuPercent.toFixed(1)}%</div>}
-          {widget.showStats && data.memUsageBytes !== null && (
+          {data.uptimeSeconds !== null && (
             <div>
-              Mem: {formatBytes(data.memUsageBytes)}
-              {data.memLimitBytes ? ` / ${formatBytes(data.memLimitBytes)}` : ""}
+              Uptime: <span className="font-mono tabular-nums text-fg">{formatUptime(data.uptimeSeconds)}</span>
+            </div>
+          )}
+          {widget.showStats && data.cpuPercent !== null && (
+            <div>
+              CPU: <span className="font-mono tabular-nums text-fg">{data.cpuPercent.toFixed(1)}%</span>
+            </div>
+          )}
+          {widget.showStats && data.memUsageBytes !== null && (
+            <div>
+              Mem:{" "}
+              <span className="font-mono tabular-nums text-fg">
+                {formatBytes(data.memUsageBytes)}
+                {data.memLimitBytes ? ` / ${formatBytes(data.memLimitBytes)}` : ""}
+              </span>
+            </div>
+          )}
+          {data.restartCount > 0 && (
+            <div>
+              Restarts: <span className="font-mono tabular-nums text-fg">{data.restartCount}</span>
             </div>
           )}
-          {data.restartCount > 0 && <div>Restarts: {data.restartCount}</div>}
         </dl>
       )}
     </div>

components/widgets/http/Widget.tsx

@@ -2,6 +2,7 @@
 
 import type { Widget } from "@/lib/config/schema";
 import { useWidgetSubscription } from "@/lib/ws/client";
+import { SkeletonLines } from "@/components/widgets/Skeleton";
 
 type HttpWidget = Extract<Widget, { type: "http" }>;
 
@@ -15,21 +16,27 @@ export function HttpWidget({ widget, widgetId }: { widget: HttpWidget; widgetId:
   const result = useWidgetSubscription(widgetId);
   const data = result?.type === "http" ? result.data : null;
   const errorMessage = result?.type === "error" ? result.message : null;
+  const pulse = data?.up ? "status-pulse" : "";
 
   return (
     <div className="flex flex-col gap-2 rounded-[var(--radius-widget)] border border-border bg-surface p-4">
       <div className="flex items-center justify-between gap-2">
         <span className="text-sm font-medium text-fg">{widget.name}</span>
         <span
-          className={`h-2.5 w-2.5 shrink-0 rounded-full ${statusColor(data?.up, data?.consecutiveFailures ?? 0)}`}
+          className={`h-2.5 w-2.5 shrink-0 rounded-full ${statusColor(data?.up, data?.consecutiveFailures ?? 0)} ${pulse}`}
           title={data ? (data.up ? "up" : `down (${data.consecutiveFailures} checks failed)`) : "unknown"}
         />
       </div>
       {errorMessage && <span className="text-xs text-status-down">{errorMessage}</span>}
+      {!result && !errorMessage && <SkeletonLines />}
       {data && (
         <dl className="flex flex-col gap-1 text-xs text-fg-muted">
-          <div>Status: {data.statusCode ?? "—"}</div>
-          <div>Latency: {data.latencyMs}ms</div>
+          <div>
+            Status: <span className="font-mono tabular-nums text-fg">{data.statusCode ?? "—"}</span>
+          </div>
+          <div>
+            Latency: <span className="font-mono tabular-nums text-fg">{data.latencyMs}ms</span>
+          </div>
           {!data.up && data.error && <div className="text-status-down">{data.error}</div>}
         </dl>
       )}

components/widgets/system/Widget.tsx

@@ -2,6 +2,7 @@
 
 import type { Widget } from "@/lib/config/schema";
 import { useWidgetSubscription } from "@/lib/ws/client";
+import { SkeletonLines } from "@/components/widgets/Skeleton";
 import { formatBytes } from "@/lib/format";
 
 type SystemWidget = Extract<Widget, { type: "system" }>;
@@ -15,13 +16,10 @@ function UsageBar({ label, percent, detail }: { label: string; percent: number;
     <div className="flex flex-col gap-1">
       <div className="flex items-center justify-between text-xs text-fg-muted">
         <span>{label}</span>
-        <span>{detail}</span>
+        <span className="font-mono tabular-nums text-fg">{detail}</span>
       </div>
       <div className="h-1.5 w-full overflow-hidden rounded-full bg-surface-raised">
-        <div
-          className="h-full rounded-full bg-accent"
-          style={{ width: `${percent}%` }}
-        />
+        <div className="h-full rounded-full bg-accent" style={{ width: `${percent}%` }} />
       </div>
     </div>
   );
@@ -36,6 +34,7 @@ export function SystemWidget({ widget, widgetId }: { widget: SystemWidget; widge
     <div className="flex flex-col gap-3 rounded-[var(--radius-widget)] border border-border bg-surface p-4 sm:col-span-2">
       <span className="text-sm font-medium text-fg">{widget.name}</span>
       {errorMessage && <span className="text-xs text-status-down">{errorMessage}</span>}
+      {!result && !errorMessage && <SkeletonLines count={3} />}
       {data && (
         <div className="flex flex-col gap-2">
           <UsageBar label="CPU" percent={data.cpuPercent} detail={`${data.cpuPercent.toFixed(1)}%`} />
@@ -51,7 +50,7 @@ export function SystemWidget({ widget, widgetId }: { widget: SystemWidget; widge
           />
           <div className="flex items-center justify-between text-xs text-fg-muted">
             <span>Network</span>
-            <span>
+            <span className="font-mono tabular-nums text-fg">
               ↓ {formatBytes(data.netRxBytesPerSec)}/s · ↑ {formatBytes(data.netTxBytesPerSec)}/s
             </span>
           </div>

components/widgets/traefik/Widget.tsx

@@ -2,6 +2,7 @@
 
 import type { Widget } from "@/lib/config/schema";
 import { useWidgetSubscription } from "@/lib/ws/client";
+import { SkeletonLines } from "@/components/widgets/Skeleton";
 
 type TraefikWidget = Extract<Widget, { type: "traefik" }>;
 
@@ -15,12 +16,13 @@ export function TraefikWidget({ widget, widgetId }: { widget: TraefikWidget; wid
       <div className="flex items-center justify-between">
         <span className="text-sm font-medium text-fg">{widget.name}</span>
         {data && (
-          <span className="text-xs text-fg-muted">
+          <span className="font-mono text-xs tabular-nums text-fg-muted">
             {data.entrypoints.map((ep) => ep.address).join(" · ") || `${data.entrypoints.length} entrypoints`}
           </span>
         )}
       </div>
       {errorMessage && <span className="text-xs text-status-down">{errorMessage}</span>}
+      {!result && !errorMessage && <SkeletonLines count={3} />}
       {data && (
         <div className="flex flex-col gap-1">
           {data.routers.map((router) => (
@@ -38,7 +40,9 @@ export function TraefikWidget({ widget, widgetId }: { widget: TraefikWidget; wid
               </span>
             </div>
           ))}
-          <span className="pt-1 text-xs text-fg-muted">{data.middlewaresCount} middlewares</span>
+          <span className="pt-1 text-xs text-fg-muted">
+            <span className="font-mono tabular-nums">{data.middlewaresCount}</span> middlewares
+          </span>
         </div>
       )}
     </div>