feat: streamline traefik widget with icon/status dot, fix grid gap

Traefik's widget was the only card without a BrandIcon or StatusDot in
its header, and had no href either - added icon/href fields to the
schema and matched the exact docker/service widget header markup.
StatusDot reuses the same "running once data loaded" convention the
other widgets already use for a non-container up/down signal.

System's widget was span=5 while every other widget in this app is
span=4 (docker/service/traefik) or 3 (http) - on a 12-column grid that
left a permanent 3-column gap next to it every row. Matched it to
span=4 so system+traefik+one more widget tile a full row exactly.
Also added grid-auto-flow: dense as a general safety net against
future span-mismatch gaps.

components/widgets/system/Widget.tsx

@@ -19,7 +19,7 @@ export function SystemWidget({ widget, widgetId }: { widget: SystemWidget; widge
   const errorMessage = result?.type === "error" ? result.message : null;
 
   return (
-    <WidgetCard span={5} rowSpan={2}>
+    <WidgetCard span={4} rowSpan={2}>
       <div className="text-[10px] tracking-[0.1em] text-accent uppercase">System</div>
       <span className="text-[15px] font-medium text-fg">{widget.name}</span>
       {errorMessage && <span className="text-xs text-status-down">{errorMessage}</span>}