feat: P1 features — quick switcher, media gallery, DM previews, knock-to-join, syntax highlighting

P1-1: Quick room switcher (Ctrl+K/Cmd+K) — QuickSwitcher.tsx + ClientNonUIFeatures hotkey
P1-2: Media gallery drawer (images/videos/files) — MediaGallery.tsx + RoomViewHeader toggle
P1-4: DM last message preview + relative timestamp in RoomNavItem when direct=true
P1-7: Code syntax highlighting — TDS tokenizer (syntaxHighlight.ts), custom CSS theme
       (.prism-tds-dark/.prism-tds-light), applied in react-custom-html-parser.tsx
P1-11: Knock-to-join — "Request to Join" in RoomIntro + Pending Requests in MembersDrawer

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

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -1,5 +1,5 @@
 import { useAtomValue } from 'jotai';
-import React, { ReactNode, useCallback, useEffect, useRef } from 'react';
+import React, { ReactNode, useCallback, useEffect, useRef, useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { RoomEvent, RoomEventHandlerMap } from 'matrix-js-sdk';
 import { roomToUnreadAtom, unreadEqual, unreadInfoToUnread } from '../../state/room/roomToUnread';
@@ -27,6 +27,7 @@ import { useSelectedRoom } from '../../hooks/router/useSelectedRoom';
 import { useInboxNotificationsSelected } from '../../hooks/router/useInbox';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
 import { usePresenceUpdater } from '../../hooks/usePresenceUpdater';
+import { QuickSwitcher } from '../../components/QuickSwitcher';
 
 function SystemEmojiFeature() {
   const [twitterEmoji] = useSetting(settingsAtom, 'twitterEmoji');
@@ -261,6 +262,26 @@ function MessageNotifications() {
   );
 }
 
+function QuickSwitcherFeature() {
+  const [open, setOpen] = useState(false);
+
+  useEffect(() => {
+    const handleKeyDown = (e: KeyboardEvent) => {
+      if ((e.ctrlKey || e.metaKey) && e.key === 'k') {
+        e.preventDefault();
+        setOpen(true);
+      }
+    };
+    window.addEventListener('keydown', handleKeyDown);
+    return () => {
+      window.removeEventListener('keydown', handleKeyDown);
+    };
+  }, []);
+
+  if (!open) return null;
+  return <QuickSwitcher onClose={() => setOpen(false)} />;
+}
+
 type ClientNonUIFeaturesProps = {
   children: ReactNode;
 };
@@ -274,6 +295,7 @@ export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
       <PresenceUpdater />
       <InviteNotifications />
       <MessageNotifications />
+      <QuickSwitcherFeature />
       {children}
     </>
   );