Panel I/O: PanelDef.io ports, scoped publish and upload, I/O section in the Panels dialog

docs/interface/dashboards.md

@@ -188,12 +188,29 @@ Several dashboards get a navigation rail.
 
 A panel credential permits its assigned dashboards, their bound messages and
 the artifacts they show. It also permits publishing from its controls and query
-charts. **Lock** changes the viewing surface; it does not narrow the credential.
+charts. On a locked dashboard only the query charts may still publish.
 
 **Unpair screen** revokes a locally paired credential and keeps the panel's
 dashboard assignments. Deleting the panel removes the assignment and its
 access.
 
+### The device's own I/O
+
+A panel can also act as a node. Under **I/O**, wire a port on the device to a
+message:
+
+| Field | Meaning |
+|---|---|
+| `port` | The device's name for it, such as `gpio.4`, `backlight`, `screen`, `touch`, `mic` or `speaker`. Lowercase letters, digits, `_` and `.` |
+| `direction` | `in`: the device publishes to the message. `out`: the device follows it |
+| `message` | A qualified `flow.name`. A flow must declare it, as for a control |
+| `config` | A JSON object passed to the device unread, such as `{"pull": "up", "debounce_ms": 50}` |
+
+The credential may publish to its `in` messages even when a dashboard is
+locked, and may upload an artifact named after one
+(`PUT /artifacts?name=<message>`), which is how a microphone sends a recording.
+`out` messages are read only.
+
 !!! note "If the local link is wrong"
 
     Pairing links use `FRONTEND_HOST`. Set it to the app address reachable