feat: Add mobile responsive layout, open room access, and admin room management

Mobile Responsive Layout:
- Add useMediaQuery, useIsMobile, useIsTablet, useIsDesktop hooks for device detection
- Create MobileHeader component with hamburger menu and action drawer
- Create BottomToolbar for mobile navigation (Files, Members)
- Create SlidePanel component for full-screen mobile sidebars
- Update RoomDetail.tsx with mobile/desktop conditional rendering
- Update RoomList.tsx with single-column grid and touch-friendly buttons
- Add CSS custom properties for safe areas and touch targets (min 44px)
- Add mobile viewport meta tags for notched devices

Open Room Access:
- All authenticated users can view all rooms (not just their own)
- Users can join active rooms they're not members of
- Add is_member field to room responses
- Update room list API to return all rooms by default

Admin Room Management:
- Add permanent delete functionality for system admins
- Add delete confirmation dialog with room title verification
- Broadcast room deletion via WebSocket to connected users
- Add users search API for adding members

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/modules/realtime/websocket_manager.py

@@ -1,12 +1,19 @@
 """WebSocket connection pool management"""
 from fastapi import WebSocket
-from typing import Dict, List, Set
+from typing import Dict, List, Set, Any
 from datetime import datetime
 import asyncio
 import json
 from collections import defaultdict
 
 
+def json_serializer(obj: Any) -> str:
+    """Custom JSON serializer for objects not serializable by default json code"""
+    if isinstance(obj, datetime):
+        return obj.isoformat()
+    raise TypeError(f"Object of type {type(obj).__name__} is not JSON serializable")
+
+
 class ConnectionInfo:
     """Information about a WebSocket connection"""
     def __init__(self, websocket: WebSocket, user_id: str, room_id: str):
@@ -93,7 +100,7 @@ class WebSocketManager:
         if room_id not in self._room_connections:
             return
 
-        message_json = json.dumps(message)
+        message_json = json.dumps(message, default=json_serializer)
 
         # Collect disconnected connections
         disconnected = []
@@ -124,7 +131,7 @@ class WebSocketManager:
             return
 
         conn_info = self._user_connections[user_id]
-        message_json = json.dumps(message)
+        message_json = json.dumps(message, default=json_serializer)
 
         try:
             await conn_info.websocket.send_text(message_json)