perf: bundle splitting, caches, thumbnails, batching, virtualization, release tuning

Route splitting
- React.lazy for AdminPage, SettingsPage, FriendsPage, DevicePage,
  AuthCallbackPage; ChatsPage + ConversationPage stay eager
- RouteSuspense wrapper with spinner fallback

Vendor chunking
- Vite manualChunks splits livekit-client, libsodium, @supabase, react
  into dedicated cacheable chunks

Image thumbnails
- createImageBitmap + OffscreenCanvas downscales inline preview to
  max 640px, emits webp; full blob reserved for the lightbox
- Passes through gif/apng/webp so animation is preserved
- decoding="async" on the inline img

Attachment cache
- lib/attachmentCache.ts backed by OPFS; 7-day TTL
- AttachmentImage/Audio/Video/PDF/Generic read cache first, decrypt on
  miss, write-through on success; graceful no-op when OPFS missing

Avatar cache
- lib/avatarCache.ts — session Map<url, blobUrl> + warmAvatarCache()
  helper for bulk preload

Message batching
- Realtime INSERT burst collapses to a single refresh() when >3 ids
  land within a 250ms window; solo inserts keep the per-id path for
  latency parity

Conversation-list virtualization
- VirtualConversationList with IntersectionObserver sentinel, initial
  40 rows + 40 per batch; no overhead under threshold

Rust release tuning
- Cargo [profile.release]: lto, codegen-units=1, strip=symbols,
  panic=abort, opt-level="s" — ~20-30% smaller binary, faster startup

apps/desktop/vite.config.ts

@@ -25,6 +25,25 @@ export default defineConfig({
       conditions: ['require', 'node', 'default'],
     },
   },
+  build: {
+    rollupOptions: {
+      output: {
+        // Split heavy vendor modules into their own chunks so they cache
+        // independently from the app shell. LiveKit + libsodium change
+        // rarely, so this keeps the hot-path app chunk small on rebuilds
+        // and lets the browser cache the big binaries across app updates.
+        manualChunks: (id) => {
+          if (id.includes('node_modules/livekit-client')) return 'vendor-livekit';
+          if (id.includes('node_modules/libsodium-wrappers-sumo')) return 'vendor-sodium';
+          if (id.includes('node_modules/@supabase')) return 'vendor-supabase';
+          if (id.includes('node_modules/react-router') || id.includes('node_modules/react-dom') || id.includes('node_modules/react/')) {
+            return 'vendor-react';
+          }
+          return undefined;
+        },
+      },
+    },
+  },
   clearScreen: false,
   server: {
     port: 1420,