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/nodes.md

@@ -256,8 +256,8 @@ To wire the loop in a flow `home`:
 
 1. Declare a [flow input](../concepts/flows.md#flow-inputs) `heard` of type
    `audio` with origin `panel`.
-2. Under the panel's [I/O](../interface/dashboards.md#the-devices-own-io), wire
-   `mic` as `in` to `home.heard` and `speaker` as `out` to `home.reply`.
+2. Add a [Device node](../interface/dashboards.md#the-devices-own-ports) for
+   the panel, publishing `mic` to `heard` and following `reply` on `speaker`.
 3. Bind the listening node's `audio` to `heard` and its `text` to `said`.
 4. Have your own nodes read `said` and publish an answer as a `str`, such as
    `answer`.