convert_session_to_image endpoint uses QueryParam instead of BodyParam, failing when called with JSON body

Same regression as BA-5496. POST /session/{session_name}/imagify handler uses QueryParam[ConvertSessionToImageRequest] instead of BodyParam.

image_name is a required field, so any client sending JSON body (e.g. WebUI) will get a validation error:

Field required [type=missing, input_value=, input_type=MultiDictProxy]

Root cause: BA-4823 (PR #9588, fc0caf8eb) bulk-changed BodyParam to QueryParam for multiple session endpoints. This was correct for GET/DELETE endpoints but incorrect for POST endpoints.

Fix:

- handler.py: Change QueryParam[ConvertSessionToImageRequest] to BodyParam[ConvertSessionToImageRequest], update query.parsed to body.parsed

- client/v2/domains/session.py: Change params= back to request= in convert_to_image method

Related: BA-5496 (rename_session — same issue)

JIRA Issue: BA-5510

Start with the POST /session/{session_name}/imagify handler in handler.py and inspect how its request is parsed. Then review client/v2/domains/session.py and the convert_to_image method. Done means JSON requests containing the required image_name field validate successfully and the client passes the request body correctly.

Written by the indexing model from the issue text.