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.

lib/config/schema.ts

@@ -62,6 +62,8 @@ export const traefikWidgetSchema = z.object({
   type: z.literal("traefik"),
   name: z.string().default("Traefik"),
   apiUrl: z.string().url(),
+  href: z.string().url().optional(),
+  icon: z.string().optional(),
   interval: durationSchema.default("15s"),
 });