fix(cli): review pass on the docsgpt command

- The image pins DOCSGPT_HOME=/app: it ships no checkout, so the data home
  no longer depends on the working directory.
- api, worker, beat and migrate print the data home and env file they
  resolved, so an API and a worker started from different directories show
  it.
- The worker passes -Q only when asked; a bare worker consumes every
  configured queue, which honours EMBEDDINGS_QUEUE and DOCUMENT_PARSE_QUEUE.
- The worker runs through celery.start and returns its exit code; click
  usage errors print usage and exit 2 instead of a traceback.
- Windows: solo pool and no embedded scheduler (celery rejects -B there),
  with a pointer to the new `docsgpt beat` command, which runs the
  scheduler on its own.
- prefetch_models and verify_offline parse their arguments, so --help is
  help rather than a model name.
- A DOCSGPT_ENV_FILE that is not a file raises instead of booting with
  defaults.

docs/content/Deploying/Pip-Install.mdx

@@ -80,7 +80,9 @@ docsgpt worker     # in a second terminal: the Celery worker, with the scheduler
 
 The API applies pending migrations when it starts (`AUTO_MIGRATE`), so `docsgpt migrate` is the explicit step for deployments that want the schema in place before the first request or that run the API with a restricted database role.
 
-The worker is not optional: query embedding runs on it, so search fails without one. `docsgpt worker --help` lists the queue, concurrency and pool options; `--no-beat` starts a worker without the scheduler when another worker already runs it.
+Both commands print the data home they resolved on start-up. Run them from the same directory, or set `DOCSGPT_HOME` for both, so the worker finds the files the API stores and the API finds the indexes the worker builds.
+
+The worker is not optional: query embedding runs on it, so search fails without one. `docsgpt worker --help` lists the queue, concurrency and pool options; `--no-beat` starts a worker without the scheduler when another worker already runs it. On Windows the scheduler cannot be embedded, so run `docsgpt beat` in a third terminal.
 
 Other commands: