fix: harden data integrity, connection stability, and memory management

Wrap all multi-write DB operations in atomic transactions (server/channel
creation, message+attachment linking, DM creation, friend acceptance,
cascading deletes) to prevent partial-write corruption.

Batch N+1 queries in WS ready payload into O(1) bulk fetches with
chunked inArray() to respect SQLite's variable limit.

Fix chat history regression where background WS messages bypassed
channel load by switching the guard from messages.has() to hasMore.has().

Add LRU channel eviction (20 cached, evict to 15) and per-channel
message cap (200) to bound client memory growth.

Shorten WS heartbeat from 30s to 15s for aggressive proxy/NAT
environments. Clear all user-scoped stores on logout to prevent
cross-session data leaks.

Extract LiveKit internal accessors into shared livekitInternals utility.

packages/web/src/hooks/useLiveKit.ts

@@ -25,6 +25,7 @@ import {
   stopScreenShare,
   handleScreenShareUnpublished,
 } from '../utils/screenShare';
+import { getMediaStreamTrack } from '../utils/livekitInternals';
 
 let _activeRoom: Room | null = null;
 
@@ -522,7 +523,7 @@ export function useLiveKit() {
         const opts = buildScreenShareOptions(screenShareConfig);
         const screenPub = room.localParticipant.getTrackPublications().find(p => p.source === Track.Source.ScreenShare);
         if (screenPub?.videoTrack) {
-          const mediaTrack = (screenPub.videoTrack as any).mediaStreamTrack as MediaStreamTrack;
+          const mediaTrack = getMediaStreamTrack(screenPub.videoTrack);
           if (mediaTrack) {
             await mediaTrack.applyConstraints({ width: { ideal: opts.capture.width }, height: { ideal: opts.capture.height }, frameRate: { ideal: opts.capture.frameRate } });
             mediaTrack.contentHint = opts.contentHint;