Both _get_access_grants and _to_prompt_model referenced an undefined
local variable 'session' instead of the 'db' parameter passed to each
method. Because these helpers are called outside of any
'async with get_async_db_context()' block, 'session' did not exist in
their scope, causing a NameError on every prompt fetch.
The NameError was silently swallowed by the broad 'except Exception'
clause in get_prompt_by_id, which returned None — causing the frontend
[id]/+page.svelte to immediately redirect back to /workspace/prompts
rather than rendering the prompt editor.
Also adds the missing 'logging' import and module-level 'log' logger,
which was referenced (but never imported) in insert_new_prompt,
update_prompt_version, and delete_prompt_by_id.
G30
48ea043f82