P3: Disable or make optional the opencode-review bot check

[SisyphusZheng]

What to build

The opencode-review bot is currently failing on PR #286 due to an API balance issue. Make it optional or fix the billing so it does not block PRs.

Acceptance criteria

• PRs are no longer blocked by bot failures.
• Bot still runs if credentials are available, or is removed.

Blocked by

None

[SisyphusZheng]

Resolved (verified): dev has no enforced required status checks — branch protection returns 404 and the only ruleset ('protect') is enforcement=disabled. The opencode-review bot therefore posts an advisory status only and cannot block PR merges (confirmed by 20+ successful squash merges this session). No code change needed. Recommendation: if a branch-protection/ruleset is ever enabled, exclude 'opencode-review' from required checks so it stays optional per project policy.