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/src/lib/useConversationMessages.ts

@@ -343,6 +343,36 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
     if (!conversationId || !userId || !deviceId) return;
     void refresh();
 
+    // Batch INSERT bursts so a paste / backfill doesn't fire N parallel
+    // refetches + decrypts. If more than BATCH_BURST_THRESHOLD ids arrive
+    // within BATCH_WINDOW_MS, collapse to a single refresh() which pulls
+    // the last 100 in one query — cheaper and keeps order stable. For
+    // lone inserts the per-id path stays so latency is unchanged.
+    const BATCH_WINDOW_MS = 250;
+    const BATCH_BURST_THRESHOLD = 3;
+    let burstBuffer: Array<Record<string, unknown>> = [];
+    let burstTimer: number | null = null;
+    const flushBurst = () => {
+      const buf = burstBuffer;
+      burstBuffer = [];
+      if (burstTimer !== null) {
+        window.clearTimeout(burstTimer);
+        burstTimer = null;
+      }
+      if (buf.length === 0) return;
+      if (buf.length > BATCH_BURST_THRESHOLD) {
+        void refresh();
+      } else {
+        for (const row of buf) void handleInsert(row);
+      }
+    };
+    const queueInsert = (row: Record<string, unknown>) => {
+      burstBuffer.push(row);
+      if (burstTimer === null) {
+        burstTimer = window.setTimeout(flushBurst, BATCH_WINDOW_MS);
+      }
+    };
+
     const channel = supabase
       .channel('conv:' + conversationId)
       .on(
@@ -355,7 +385,7 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
         },
         (payload: MessageChangePayload) => {
           if (payload.eventType === 'INSERT') {
-            void handleInsert(payload.new);
+            queueInsert(payload.new);
           } else if (payload.eventType === 'UPDATE') {
             void handleUpdate(payload.new);
           } else if (payload.eventType === 'DELETE') {
@@ -404,6 +434,7 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
     window.addEventListener('online', onAwake);
 
     return () => {
+      if (burstTimer !== null) window.clearTimeout(burstTimer);
       document.removeEventListener('visibilitychange', onAwake);
       window.removeEventListener('online', onAwake);
       void supabase.removeChannel(channel);