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>

openspec/changes/archive/2025-12-04-add-open-room-access/proposal.md

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+# Proposal: Add Open Room Access
+
+## Summary
+Modify the room access model to allow all authenticated users to view and self-join rooms, while maintaining role-based permissions for room operations.
+
+## Motivation
+The current room model requires explicit invitation for users to see and join rooms. This creates friction in incident response scenarios where speed is critical. Users should be able to:
+1. Discover all active incidents without needing an invitation
+2. Self-join rooms to contribute or observe
+3. Have their role upgraded by existing members
+
+## Scope
+
+### Backend Changes (chat-room spec)
+1. **Public Room Listing**: All authenticated users can view all rooms (not just their own)
+2. **Self-Join Mechanism**: New endpoint `POST /api/rooms/{room_id}/join` for self-joining as VIEWER
+3. **Role Upgrade Permission**: EDITOR role gains permission to upgrade VIEWER → EDITOR
+
+### Frontend Changes (frontend-core spec)
+1. **Member Search**: Add user search functionality when inviting/managing members
+2. **Password Visibility Toggle**: Add show/hide password button on login form
+3. **Join Room Button**: Display "Join" button for rooms where user is not a member
+
+## Out of Scope
+- Creating private/invite-only room types (future enhancement)
+- Role downgrade by EDITOR (only OWNER can downgrade)
+- Member removal by EDITOR (only OWNER can remove)
+
+## Related Specs
+- `chat-room`: Room membership and access control
+- `frontend-core`: Login and member management UI