feat: P1 features — voice speed, private receipts, room filter, favorites, invite link, poll creation

P1-5: Voice message playback speed toggle (0.75×/1×/1.5×/2×) in AudioContent.tsx
P1-10: Private read receipts toggle in Privacy settings; wired to notifications.ts
P1-3: Room filter input on Home tab and DMs tab (client-side, clears on tab switch)
P1-8: Favorite rooms via m.favourite tag — Favorites section in Home sidebar, star/unstar in right-click menu
P1-9: Room invite link + QR code in room settings (Share Room tile, api.qrserver.com QR)
P1-6: Poll creation modal in composer (PollCreator.tsx, sends m.poll.start)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/state/settings.ts

@@ -45,6 +45,7 @@ export interface Settings {
   pageZoom: number;
   hideActivity: boolean;
   hidePresence: boolean;
+  privateReadReceipts: boolean;
   presenceStatus: 'auto' | 'online' | 'idle' | 'dnd' | 'invisible';
 
   isPeopleDrawer: boolean;
@@ -93,6 +94,7 @@ const defaultSettings: Settings = {
   pageZoom: 100,
   hideActivity: false,
   hidePresence: false,
+  privateReadReceipts: false,
   presenceStatus: 'auto',
 
   isPeopleDrawer: true,