feat(web): stale-while-revalidate caches to eliminate tab-switch flicker

Sidebar tabs, Settings, and drill-in detail pages re-fetched on every
visit (loading=true + onMount), flashing an empty skeleton frame on each
navigation. Add an SWR cache layer so revisiting a view renders cached
data instantly while refreshing in the background.

- resourceCache.ts: single-value + keyed (per-id) SWR cache factories
- caches.ts: per-resource cache instances; resetAllCaches() on logout
- eventsSnapshot.ts: warm-seed snapshot for the SSE/paginated events page
- List/sidebar pages read $cache.value via $derived, refresh() on mount;
  mutations refresh the cache
- Settings forms seed once from settingsCache (edit-safe) and refetch
  after save (PUT /api/settings returns {status}, not the Settings object)
- Detail [id] pages warm-seed per id; apps/[id] seeds {workload,containers},
  resets non-seeded panels on warm nav, clears workload on 404, and
  invalidates its cache entry on delete

Deferred (still cold-fetch): triggers/[id] (webhook secret + multi-fetch
body gate), apps/new (create wizard).

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

@@ -10,6 +10,7 @@
 	import { toasts } from '$lib/stores/toast';
 	import { connectGlobalEvents, toEventLogEntry, type SSEConnection, type EventLogSSEPayload } from '$lib/sse';
 	import type { EventLogEntry, EventLogStats } from '$lib/types';
+	import { getEventsSnapshot, saveEventsSnapshot } from '$lib/stores/eventsSnapshot';
 	import EventLogEntryComponent from '$lib/components/EventLogEntry.svelte';
 	import EventLogFilter from '$lib/components/EventLogFilter.svelte';
 	import EmptyState from '$lib/components/EmptyState.svelte';
@@ -18,9 +19,13 @@
 
 	// ── State ─────────────────────────────────────────────────────
 
-	let events = $state<EventLogEntry[]>([]);
-	let stats = $state<EventLogStats>({ info: 0, warn: 0, error: 0, total: 0 });
-	let loading = $state(true);
+	// Warm-start from the last-known snapshot so switching back to this tab
+	// paints the previous events immediately instead of a skeleton; a
+	// background refresh in onMount then brings it current. See eventsSnapshot.ts.
+	const seed = getEventsSnapshot();
+	let events = $state<EventLogEntry[]>(seed?.events ?? []);
+	let stats = $state<EventLogStats>(seed?.stats ?? { info: 0, warn: 0, error: 0, total: 0 });
+	let loading = $state((seed?.events.length ?? 0) === 0);
 	let loadingMore = $state(false);
 	let hasMore = $state(true);
 	let newEventIds = $state<Set<number>>(new Set());
@@ -61,7 +66,10 @@
 		const currentOffset = append ? offset : 0;
 		if (append) {
 			loadingMore = true;
-		} else {
+		} else if (events.length === 0) {
+			// Only show the skeleton on a true cold load. When we already have
+			// (seeded or previously loaded) events, refresh in place so the list
+			// never blanks out — this is what removes the tab-switch flicker.
 			loading = true;
 		}
 
@@ -135,6 +143,13 @@
 		loadEvents();
 	}
 
+	// Mirror the current list + stats into the module snapshot so the next
+	// visit can warm-start. Cheap (stores references); keeps the snapshot fresh
+	// through loads, SSE pushes, and deletes without touching each mutation site.
+	$effect(() => {
+		saveEventsSnapshot({ events, stats });
+	});
+
 	// ── Client-side text filter ──────────────────────────────────
 
 	const filteredEvents = $derived(