Panels become devices: per-device documents in the flow repo, a Devices tab

- flow/devices.py: DeviceDef in FLOWS_DIR/_devices/<id>.json, committed under
  the flow store's write lock, 409 on a stale version; nonces in DEVICES_FILE
  outside git; in-memory presence announced as device_status
- api/routes/devices.py: CRUD, pairing with an optional {name, board,
  firmware}, a pending list adopted without a code from the LAN only, unpair;
  /panels/pair, /panels/pair/{code} and GET /panels/{id} kept as aliases,
  PUT /panels/ gone
- _device_may replaces _panel_may, JWT claims unchanged
- panels.json moves into devices once at startup, then .migrated
- MCP list_devices, get_device; search category device
- Devices tab (list, detail with presence, pairing, ordered dashboards,
  touch, I/O), PanelsDialog removed, serialised optimistic saves

docs/code/agents.md

@@ -39,6 +39,7 @@ instance from the portal first if this browser has not recently.
 | Inspect flows | `list_flows`, `get_flow`, `get_node_source`, `list_node_types`, `get_graph`, `list_shared_nodes` |
 | Inspect values | `get_flow_state`, `get_message_history` |
 | Inspect the instance | `list_secrets` (names only), `get_modules`, `get_health`, `get_metrics`, `list_failures`, `list_runs` (live cascades) |
+| Inspect devices | `list_devices`, `get_device` |
 | Edit flows | `save_flow`, `save_node_source`, `validate_flow`, `publish_flow`, `discard_draft`, `delete_flow` |
 | Operate flows | `run_flow`, `trigger_node`, `start_flow`, `stop_flow`, `pause_flow`, `resume_flow`, `cancel_node` |
 | Install node packages | `apply_modules` |