A node's worker label is worker, so a device is only a paired one

- NodeDef `device`/`device_policy` become `worker`/`worker_policy`, the
  issue `ignored_device` becomes `ignored_worker`, and the SDK's `@node`
  takes `worker=` and `worker_policy=`
- FlowStore._migrate renames the keys in published and draft documents
  once, bumping their version; a queued run's `needs` reads the old key
- placement passes the label as `label`, client regenerated
- docs: worker placement wording, MCP issuer without DOMAIN, device rows in
  the CLI data directory and the API table, device links in compose comments

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/code/nodes.md

@@ -324,10 +324,10 @@ waiting for that deadline.
 
 ## Running a node somewhere else
 
-Set a device label to select an attached worker:
+Set a worker label to select an attached worker:
 
 ```json
-{"id": "train", "device": "gpu", "device_policy": "require", "timeout": 7200}
+{"id": "train", "worker": "gpu", "worker_policy": "require", "timeout": 7200}
 ```
 
 `require` is the default and waits for a worker with that label. `prefer` uses