feat: add health indicator and localhost auto-detect

Surfaces live connection health for the active instance in the sidebar
and probes localhost:8000 on the first-run choose-type screen so users
running Honcho locally can connect in one tap.

- useHealthStatus hook polls checkConnection every 30s via TanStack Query
- HealthDot component renders a colored status dot with tooltip
- choose-type screen silently probes http://localhost:8000 once; on
  success it surfaces a "Detected Honcho at localhost:8000 — tap to
  connect" banner that opens the self-hosted form

packages/web/src/hooks/useHealthStatus.ts

@@ -0,0 +1,20 @@
+import { useQuery } from "@tanstack/react-query";
+import { useInstances } from "@/hooks/useInstances";
+import { checkConnection } from "@/lib/config";
+
+const POLL_INTERVAL_MS = 30_000;
+
+export function useHealthStatus() {
+	const { active } = useInstances();
+	return useQuery({
+		queryKey: ["health", active?.id, active?.baseUrl, active?.token],
+		queryFn: async () => {
+			if (!active) throw new Error("No active instance");
+			return checkConnection(active.baseUrl, active.token || undefined);
+		},
+		enabled: !!active,
+		refetchInterval: POLL_INTERVAL_MS,
+		refetchOnWindowFocus: true,
+		staleTime: 0,
+	});
+}