A test pins "Fetch now" on a prompt source: an unknown source, or a forge whose prompts routine is off, is refused and nothing runs

runPromptSource in src/actions/prompts.ts refuses no_such_source and not_running, and no test names not_running.

Done:

[ ] A new test: a repository admin presses Fetch now on their source while the routine runs (stub it), and one fetch happens.
[ ] On a forge with no prompts routine, the answer is not_running, and nothing is fetched.
[ ] A source id of another repository is no_such_source.
[ ] A writer who is not an admin is refused.

Files: test/prompt-fetch-now.test.ts

If the test finds the behaviour wrong, fix the action in the same pull and say so.

If the check fails in a test this pull does not touch, name it in the pull rather than widening the change.

Before pushing: bun x tsc --noEmit and the tests this names.

A test pins "Fetch now" on a prompt source: an unknown source, or a forge whose prompts routine is off, is refused and nothing runs #7119