feat: global Docker health indicator and graceful degradation

- GET /api/health endpoint returning Docker connectivity status
- Sidebar shows Docker connection dot (green=connected, red=disconnected)
- Stale scanner returns store-only results when Docker is unavailable
- Polls health every 30s

web/src/routes/+layout.svelte

@@ -8,6 +8,8 @@
 	import LocaleSwitcher from '$lib/components/LocaleSwitcher.svelte';
 	import { IconDashboard, IconProjects, IconDeploy, IconProxies, IconEvents, IconSettings, IconMenu, IconX, IconLogout } from '$lib/components/icons';
 	import { connectGlobalEvents, type SSEConnection } from '$lib/sse';
+	import { isAuthenticated, clearAuth } from '$lib/auth';
+	import * as api from '$lib/api';
 	import { instanceStatusStore } from '$lib/stores/instance-status';
 	import { resolvedTheme, applyTheme } from '$lib/stores/theme';
 	import { t } from '$lib/i18n';
@@ -34,6 +36,8 @@
 
 	let sseConnection: SSEConnection | null = null;
 	let sidebarOpen = $state(false);
+	let dockerConnected = $state<boolean | null>(null);
+	let healthInterval: ReturnType<typeof setInterval> | null = null;
 
 	// Hide sidebar and chrome on the login page.
 	const isLoginPage = $derived($page.url.pathname === '/login');
@@ -59,28 +63,41 @@
 	});
 
 	function logout() {
-		if (typeof localStorage !== 'undefined') {
-			localStorage.removeItem('auth_token');
-		}
+		clearAuth();
 		sseConnection?.close();
 		sseConnection = null;
 		window.location.href = '/login';
 	}
 
 	onMount(() => {
-		sseConnection = connectGlobalEvents({
-			onInstanceStatus(payload) {
-				instanceStatusStore.update(payload);
-			},
-			onDeployStatus(payload) {
-				instanceStatusStore.notifyDeploy(payload);
+		if (isAuthenticated()) {
+			sseConnection = connectGlobalEvents({
+				onInstanceStatus(payload) {
+					instanceStatusStore.update(payload);
+				},
+				onDeployStatus(payload) {
+					instanceStatusStore.notifyDeploy(payload);
+				}
+			});
+
+			// Poll Docker health every 30s.
+			async function checkHealth() {
+				try {
+					const h = await api.getHealth();
+					dockerConnected = h.docker;
+				} catch {
+					dockerConnected = null;
+				}
 			}
-		});
+			checkHealth();
+			healthInterval = setInterval(checkHealth, 30_000);
+		}
 	});
 
 	onDestroy(() => {
 		sseConnection?.close();
 		sseConnection = null;
+		if (healthInterval) clearInterval(healthInterval);
 	});
 </script>
 
@@ -156,6 +173,17 @@
 
 		<!-- Footer controls -->
 		<div class="space-y-3 border-t border-[var(--border-primary)] px-4 py-3">
+			{#if dockerConnected !== null}
+				<div class="flex items-center gap-2 rounded-md px-2 py-1.5 text-xs {dockerConnected ? 'text-emerald-600' : 'text-red-500'}">
+					<span class="relative flex h-2 w-2">
+						{#if dockerConnected}
+							<span class="absolute inline-flex h-full w-full animate-ping rounded-full bg-emerald-400 opacity-50"></span>
+						{/if}
+						<span class="relative inline-flex h-2 w-2 rounded-full {dockerConnected ? 'bg-emerald-500' : 'bg-red-500'}"></span>
+					</span>
+					Docker {dockerConnected ? $t('health.connected') : $t('health.disconnected')}
+				</div>
+			{/if}
 			<div class="flex items-center justify-between">
 				<ThemeToggle />
 				<LocaleSwitcher />