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/auth/services/user_service.py

@@ -87,3 +87,31 @@ def get_display_name(db: Session, user_id: str) -> str:
     if user:
         return user.display_name
     return user_id  # Fallback to email if user not in database
+
+
+def search_users(db: Session, query: str, limit: int = 20) -> list[User]:
+    """Search users by display_name or user_id (email)
+
+    Args:
+        db: Database session
+        query: Search query string
+        limit: Maximum number of results (default 20)
+
+    Returns:
+        List of matching users
+    """
+    from sqlalchemy import or_
+
+    search_pattern = f"%{query}%"
+
+    return (
+        db.query(User)
+        .filter(
+            or_(
+                User.display_name.ilike(search_pattern),
+                User.user_id.ilike(search_pattern)
+            )
+        )
+        .limit(limit)
+        .all()
+    )