Device node: a device's ports are wired in flows

- flow/nodes/device.py: `device` node with params `device` and `config`;
  provides the device's `in` ports, requires its `out` ports without
  waking anything, never run (Node.passive), down "Offline" from presence
- DeviceDef.io and DevicePort go; GET /devices/{id} computes `io` and
  `bindings` from the device nodes of published flows, in a fixed order,
  cached by FlowStore.revision; the credential's scope comes from them
- issues `unknown_device` and `device_port` (wired twice; against a report
  the wrong direction or dtype, or unlisted as advisory), rechecked when a
  device is created or deleted; ValidationIssue.advisory is a field
- a device publishing on a bound port is credited to its node by the
  server; the panel endpoint kind is gone from `_endpoints` and the canvas
- a rebuild that moves a device's bindings sends `dashboard_changed` with
  an empty name, which the firmware refetches on
- startup moves each device's `io` rows into device nodes in the flows
  declaring their messages, draft and published, one commit; rows no
  flow declares are logged and left out
- frontend: Device node settings (device, Publishes, Follows, a port
  picker from a report), palette shortcuts per reported port, DeviceDetail
  lists bindings with "Use in flow" in place of the I/O editor
- docs: devices, flow editor, node types, issues, API

docs/code/api.md

@@ -191,7 +191,7 @@ on its own, so this is for reclaiming space sooner.
 | `POST` | `/dashboards/{name}/publish`, `/dashboards/{name}/discard`, `/dashboards/{name}/rename` | publish, discard, or rename |
 | `POST` | `/dashboards/{name}/duplicate` | copy into an unpublished `{name}_copy` |
 | `GET` | `/devices/` | list devices, with `online` and `last_seen` |
-| `POST`, `GET`, `PUT`, `DELETE` | `/devices/{id}` | create, read, save or delete one; a save sends the `version` it read and gets 409 when someone saved first |
+| `POST`, `GET`, `PUT`, `DELETE` | `/devices/{id}` | create, read, save or delete one; a save sends the `version` it read and gets 409 when someone saved first. A read adds `io` and `bindings`, its ports as the device nodes of published flows wire them |
 | `POST` | `/devices/pair` | start device pairing, optionally with `{name, board, firmware}`; unauthenticated |
 | `GET` | `/devices/pair/{code}` | poll pairing with its `secret`; answers `device` (and `panel` for older firmware); unauthenticated |
 | `GET` | `/devices/pending` | devices waiting for a code, as they describe themselves |