feat: integrate Matrix chat (Option 2 - credentials stored in Supabase)

- Add matrix-js-sdk, marked, highlight.js, twemoji, @tanstack/svelte-virtual deps
- Copy Matrix core layer: /matrix/, /stores/matrix.ts, /cache/, /services/
- Copy Matrix components: matrix/, message/, chat-layout/, chat-settings/
- Copy UI components: EmojiPicker, Twemoji, ImagePreviewModal, VirtualList
- Copy utils: emojiData, twemoji, twemojiGlobal
- Replace lucide-svelte with Material Symbols in SyncRecoveryBanner
- Extend Avatar with xs size and status indicator prop
- Fix ui.ts store conflict: re-export toasts from toast.svelte.ts
- Add migration 020_matrix_credentials for storing Matrix tokens per user/org
- Add /api/matrix-credentials endpoint (GET/POST/DELETE)
- Create [orgSlug]/chat page with Matrix login form + full chat UI
- Add Chat to sidebar navigation

src/lib/components/ui/index.ts

@@ -26,3 +26,7 @@ export { default as Icon } from './Icon.svelte';
 export { default as AssigneePicker } from './AssigneePicker.svelte';
 export { default as ContextMenu } from './ContextMenu.svelte';
 export { default as PageSkeleton } from './PageSkeleton.svelte';
+export { default as ImagePreviewModal } from './ImagePreviewModal.svelte';
+export { default as Twemoji } from './Twemoji.svelte';
+export { default as EmojiPicker } from './EmojiPicker.svelte';
+export { default as VirtualList } from './VirtualList.svelte';