Add ScreenConnect-parity features (high + medium)

Viewer:
- Toolbar: Ctrl+Alt+Del, clipboard paste, monitor picker, file transfer, chat, WoL buttons
- Multi-monitor: agent sends monitor_list on connect, viewer can switch via dropdown
- Clipboard sync: agent polls local clipboard → sends to viewer; viewer paste → agent sets remote clipboard
- File transfer panel: drag-drop upload to agent, directory browser, download files from remote
- Chat panel: bidirectional text chat forwarded through relay

Agent:
- Multi-monitor capture with set_monitor/set_quality message handlers
- exec_key_combo for Ctrl+Alt+Del and arbitrary combos
- Clipboard polling via pyperclip (both directions)
- File upload/download/list_files with base64 chunked protocol
- Attended mode (--attended): zenity/kdialog/PowerShell consent dialog before accepting stream
- Auto-update: heartbeat checks version, downloads new binary and exec-replaces self (Linux)
- Reports MAC address on registration (for WoL)

Relay:
- Forwards monitor_list, clipboard_content, file_chunk, file_list, chat_message agent→viewer
- Session recording: when RECORDING_DIR env set, saves JPEG frames as .remrec files
- ALLOWED_ORIGINS CORS now set from NEXT_PUBLIC_APP_URL in docker-compose

Database:
- groups table (id, name, description, created_by)
- machines: group_id, mac_address, notes, tags text[]
- Migration 0003 applied

Dashboard:
- Machines page: search, tag filter, group filter, inline notes/tags/rename editing
- MachineCard: inline tag management, group picker, notes textarea
- Admin page: new Groups tab (create/list/delete groups)
- API: PATCH /api/machines/[id] (name, notes, tags, groupId)
- API: GET/POST/DELETE /api/groups
- API: POST /api/machines/wol (broadcast magic packet)

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

docker-compose.yml

@@ -12,6 +12,8 @@ services:
     volumes:
       - postgres_data:/var/lib/postgresql/data
       - ./db/migrations/0001_initial.sql:/docker-entrypoint-initdb.d/0001_initial.sql:ro
+      - ./db/migrations/0002_agent_relay.sql:/docker-entrypoint-initdb.d/0002_agent_relay.sql:ro
+      - ./db/migrations/0003_enhancements.sql:/docker-entrypoint-initdb.d/0003_enhancements.sql:ro
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-remotelink}"]
       interval: 10s