[TheGreatAxios]

Closes CL-10919

What changed

• New rule check: conventional-commits (no model). The pull request title and each commit's first line (first 100 commits) must read type(scope)!: subject with an allowed type (case-insensitive, per the spec); merge commits and GitHub's Revert "…" subjects are skipped, in the title and the commits. Options: types to override the default list (feat, fix, refactor, perf, docs, test, chore, ci, build, style, revert) and fields: [title, commits] (default both).
• A failure names up to three offenders, e.g. "Add tests for live run stream isn't a conventional commit", then "and N more".
• No new host calls: GitHub and Bitbucket Data Center already read commits.
• The setup skill's phrase-based conventional-title recipe is replaced by the built-in rule; PRODUCT and the user manual's Rules section updated.

How it was verified

• bun run check; contracts 113, triage-workflows 194, web lib 197, policy-check-action 2.
• Tests through the real policy file: scope with !, merge commits skipped, bad type, missing colon or space, custom types, title only. End-to-end test shaped like feat(chat): stream live run progress and render saved inference traces workbench#1125 gives Fail naming the three commits.
• Judge requests unchanged: the 54 eval cases (186 requests) are byte-identical on main and here.

[linear-code]

CL-10919

[corbits-triage]

Triage: Pass

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