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/reference/configuration.md

@@ -23,7 +23,8 @@ For CLI installations, select storage with `--data-dir`, `FLUKSIO_HOME` or
 | `ALERTS_FILE` | `$DATA_DIR/alerts.json` | alert channels and rules |
 | `WEBPUSH_FILE` | `$DATA_DIR/webpush.json` | push keys and browser subscriptions |
 | `PROVISIONERS_FILE` | `$DATA_DIR/provisioners.json` | optional worker provisioning configuration |
-| `PANELS_FILE` | `$DATA_DIR/panels.json` | wall-panel pairings |
+| `DEVICES_FILE` | `$DATA_DIR/devices.json` | device credential nonces, outside the flow repository |
+| `PANELS_FILE` | `$DATA_DIR/panels.json` | panels of an instance from before devices, moved into devices on first start and renamed `.migrated` |
 | `OAUTH_PRIVATE_KEY_FILE` | `$DATA_DIR/oauth-key.pem` | agent and worker signing key |
 | `CLOUD_CONFIG_FILE` | `$DATA_DIR/cloud.json` | optional portal enrollment |
 | `AI_CONFIG_FILE` | `$DATA_DIR/ai.json` | optional assistant provider configuration |

docs/reference/payload-types.md

@@ -170,4 +170,4 @@ port and received value. It is not published downstream.
 
 - [Flows, nodes and messages](../concepts/flows.md)
 - [Node types](node-types.md)
-- [Dashboards and panels](../interface/dashboards.md)
+- [Dashboards and devices](../interface/dashboards.md)