feat: live docker/database widgets over WebSocket (M2)

Adds a custom server.ts (http server + Next request handler + a
noServer:true WebSocket server on /ws) so the app can push live data
without polling. A CollectorScheduler runs one interval-based job per
docker/database widget instance, backed by dockerode against
/var/run/docker.sock, and reconciles jobs when config.yml changes.

Config hot-reload is now fully wired: chokidar watches config.yml/.env,
re-validates on change, and broadcasts config:update (or a
non-destructive config:error, keeping the last-good config) to every
connected browser. The client subscribes to per-widget topics over a
single shared WebSocket with exponential-backoff reconnect and
last-result caching for instant resubscribe.

Verified end-to-end against real throwaway containers (nginx, redis):
live CPU/mem/uptime/health streamed over the socket, interval changes
picked up without a server restart, and a broken config.yml correctly
falls back to the last-valid config instead of crashing the app.

components/widgets/database/Widget.tsx

@@ -0,0 +1,33 @@
+"use client";
+
+import type { Widget } from "@/lib/config/schema";
+import { useWidgetSubscription } from "@/lib/ws/client";
+import { StatusDot } from "@/components/widgets/StatusDot";
+import { formatUptime } from "@/lib/format";
+
+type DatabaseWidget = Extract<Widget, { type: "database" }>;
+
+const ENGINE_LABEL: Record<DatabaseWidget["engine"], string> = {
+  postgres: "PostgreSQL",
+  redis: "Redis",
+};
+
+export function DatabaseWidget({ widget, widgetId }: { widget: DatabaseWidget; widgetId: string }) {
+  const result = useWidgetSubscription(widgetId);
+  const data = result?.type === "database" ? result.data : null;
+  const errorMessage = result?.type === "error" ? result.message : null;
+
+  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>
+        <StatusDot status={data?.status} health={data?.health} />
+      </div>
+      <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>
+      )}
+    </div>
+  );
+}