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/MatrixProvider.svelte

@@ -0,0 +1,32 @@
+<script lang="ts">
+  import { onMount, onDestroy } from "svelte";
+  import type { Snippet } from "svelte";
+  import type { MatrixClient } from "matrix-js-sdk";
+  import { setMatrixContext } from "$lib/matrix/context";
+  import { setupSyncHandlers, removeSyncHandlers } from "$lib/matrix/sync";
+
+  interface Props {
+    client: MatrixClient;
+    children: Snippet;
+  }
+
+  let { client, children }: Props = $props();
+
+  // Store client reference for cleanup
+  let clientRef = client;
+
+  // Set the context during component initialization
+  setMatrixContext(clientRef);
+
+  // Setup sync handlers when provider mounts
+  onMount(() => {
+    setupSyncHandlers(clientRef);
+  });
+
+  // Cleanup when provider unmounts
+  onDestroy(() => {
+    removeSyncHandlers(clientRef);
+  });
+</script>
+
+{@render children()}