fix: resolve ERR_INSUFFICIENT_RESOURCES connection exhaustion

- Add concurrency limiter (max 4 GET requests) to API layer, leaving
  slots for SSE and health checks. Write ops bypass the limiter.
- Add AbortController to ContainerStats, project detail page, and
  dashboard to cancel in-flight requests on navigation/unmount.
- Move global SSE connection from layout to events page (only consumer).
- Add 30s heartbeat to SSE endpoint to detect zombie connections.
- Serialize dashboard project fetches to avoid parallel burst.
- Rebuild frontend in dev-server.sh so go:embed stays in sync.

web/src/routes/events/+page.svelte

@@ -8,8 +8,7 @@
 	import { fetchEventLog, fetchEventLogStats, clearAllEvents, deleteEvent } from '$lib/api';
 	import ConfirmDialog from '$lib/components/ConfirmDialog.svelte';
 	import { toasts } from '$lib/stores/toast';
-	import { subscribeEventLog } from '$lib/stores/event-log-bus';
-	import type { EventLogSSEPayload } from '$lib/sse';
+	import { connectGlobalEvents, type SSEConnection, type EventLogSSEPayload } from '$lib/sse';
 	import type { EventLogEntry, EventLogStats } from '$lib/types';
 	import EventLogEntryComponent from '$lib/components/EventLogEntry.svelte';
 	import EventLogFilter from '$lib/components/EventLogFilter.svelte';
@@ -36,7 +35,7 @@
 	const PAGE_SIZE = 50;
 	let offset = $state(0);
 
-	let unsubscribeEventLog: (() => void) | null = null;
+	let sseConnection: SSEConnection | null = null;
 	let listEl: HTMLDivElement | undefined = $state();
 	let showClearConfirm = $state(false);
 
@@ -199,15 +198,17 @@
 		loadEvents();
 		loadStats();
 
-		// Subscribe to event_log events from the global SSE connection (no duplicate connection).
-		unsubscribeEventLog = subscribeEventLog((payload: EventLogSSEPayload) => {
-			handleSSEEvent(payload);
+		// Open SSE connection only while this page is mounted.
+		sseConnection = connectGlobalEvents({
+			onEventLog(payload) {
+				handleSSEEvent(payload);
+			}
 		});
 	});
 
 	onDestroy(() => {
-		unsubscribeEventLog?.();
-		unsubscribeEventLog = null;
+		sseConnection?.close();
+		sseConnection = null;
 	});
 </script>