Fix the code-contribution fork fallback (v0.5.1)

[Barneyjm]

What broke

A runner hit this mid-task:

! code PR failed (gh repo exited 1: the `--remote` flag is unsupported when a
repository argument is provided) — submitting with code inline only

publishCodeContribution fell back to gh repo fork <repo> --remote --remote-name contribfork
whenever the direct push to the contrib repo was refused. gh rejects --remote outright when a
repository argument is present, so the fork step exited 1, the PR never opened, and the
contribution degraded to inline code only.

No volunteer work was lost — the inline copy is persisted server-side either way — but the
artifact_uri never became a PR URL.

The fix

Fork without touching remotes, then wire the fork up with plain git:

await run('gh', ['repo', 'fork', repo, '--clone=false'], dir);
const login = (await run('gh', ['api', 'user', '--jq', '.login'], dir)).trim();
await run('git', ['remote', 'add', 'contribfork', `https://github.com/${login}/${name}.git`], dir);
await run('git', ['push', '-u', 'contribfork', branch], dir);

The gh api user call moved ahead of the push, since the login now builds the remote URL.

Also: the direct-push error is no longer swallowed. Previously only the fork failure surfaced,
hiding why the push was refused. The runner now reports both causes:
direct push refused (…); fork fallback failed (…).

Verification

Against real gh 2.88.1 and real GitHub, using an upstream without push rights that was already
forked (so the fork step added nothing new):

• Old form reproduces the reported error exactly, at flag validation.
• git push -u origin → remote: Permission to rkbarney/justrss.git denied to Barneyjm (403), so
  the fallback genuinely triggers.
• gh repo fork rkbarney/justrss --clone=false → Barneyjm/justrss already exists, exit 0.
• git remote add contribfork → git push -u contribfork → * [new branch].

head resolves to Barneyjm:contrib/…, exactly what gh pr create --head wants. Only
gh pr create was skipped, since it would open a PR on a third party's repo. Rehearsal branch
deleted afterward.

Notes

• Version bumped to 0.5.1 (rides this PR, per convention). The lockfile root still said 0.4.0 —
  never bumped for 0.5.0 — so that drift is corrected here too.
• Runners install via npx givework start, so this only reaches volunteers on release.

🤖 Generated with Claude Code

https://claude.ai/code/session_01WoAJRWLbAW5pakUUzEzcjV