- artifacts automatically stick to user session

[wolfy-j]

This pull request refactors how the user_id is determined when creating an artifact in the artifact_repo.create function. The main improvement is ensuring that the user_id is always associated with the session if a valid session_id is provided, otherwise it falls back to the authenticated actor. This change improves data consistency and aligns artifact ownership with session context.

Session handling and user association:

• The logic for determining user_id now checks if a valid session_id is provided; if so, it retrieves user_id from the session record, otherwise it uses the authenticated actor's ID. [1] [2]
• The session existence check now selects both session_id and user_id from the sessions table, ensuring the correct user association for artifacts created within a session.

Code clarity and cleanup:

• Removed redundant comments and streamlined code for building and executing the artifact insertion query, making the function easier to read and maintain.