Replace git-commit-conventions with user-invocable commit skill

[williamthorsen]

Parent: #277

Problem

Agents frequently violate commit message conventions: using process-oriented titles ("Address review findings"), including finding IDs (F1, W2), referencing automated tests, omitting backtick formatting for code identifiers, and not punctuating list items in the body. The existing git-commit-conventions skill is non-user-invocable and gets ignored by both the main agent and subagents.

Context

The git-commit-conventions skill at packages/agents/content/skills/git-commit-conventions/SKILL.md is listed as a skill dependency in the orchestrated-coder subagent. The reference data file _data/commit-format.md covers title format and length. Neither covers the body formatting rules that cause the most cleanup work.

Solution

Replace the git-commit-conventions skill directory with a commit skill directory. Make it user-invocable so it appears in the skill list and is more likely to be invoked. Expand the conventions to include all rules from the issue:

Title rules (existing + reinforced):

• 72 chars max (hard limit)
• {workspace}|{work type}: {description} format
• No ticket ID
• Describes the code change, not the process

Body rules (new):

• Punctuate list items: each bulleted item ends with a period, comma, or semicolon.
• Break up large paragraphs; blank line between paragraphs.
• Use backticks for code identifiers (methodName, MyClass, path/to/file).
• Never reference automated tests/CI (formatting, linting, unit tests, typechecking).
• Never use review finding IDs (F1, W2, T3, etc.) — these are meaningful only in review documents.

Skill references update:

• Update orchestrated-coder: git-commit-conventions → commit in its skills list.
• Update common-mistakes: cross-reference the new skill name.
• Update _data/commit-format.md to include body formatting rules.
• Delete the git-commit-conventions/ directory.

Acceptance criteria

• commit skill exists at packages/agents/content/skills/commit/SKILL.md with user-invocable: true
• All title and body rules from the issue are covered
• git-commit-conventions/ directory is deleted
• All subagent references updated from git-commit-conventions to commit
• common-mistakes cross-references updated
• _data/commit-format.md updated with body formatting rules