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/matrix/index.ts

@@ -0,0 +1,12 @@
+export { default as MessageList } from './MessageList.svelte';
+export { default as MessageInput } from './MessageInput.svelte';
+export { default as TypingIndicator } from './TypingIndicator.svelte';
+export { default as CreateRoomModal } from './CreateRoomModal.svelte';
+export { default as CreateSpaceModal } from './CreateSpaceModal.svelte';
+export { default as MemberList } from './MemberList.svelte';
+export { default as StartDMModal } from './StartDMModal.svelte';
+export { default as RoomInfoPanel } from './RoomInfoPanel.svelte';
+export { default as RoomSettingsModal } from './RoomSettingsModal.svelte';
+export { default as UserProfileModal } from './UserProfileModal.svelte';
+export { default as MatrixProvider } from './MatrixProvider.svelte';
+export { default as SyncRecoveryBanner } from './SyncRecoveryBanner.svelte';