ci: enforce branch model, conventional commits, and no-AI-files policy

[ss-o]

What this does

Applies the full repository governance setup to keep zi's history clean, professional, and contributor-friendly.

Changes

File	What changed
.github/copilot-instructions.md	New — Copilot config: commit format, branch model, no AI co-author trailers, no AI config files
.github/workflows/commit-lint.yml	New — CI that validates conventional commits, blocks AI co-author trailers, checks PR title and branch name
.github/workflows/trunk-check.yml	Run Trunk on next branch as well as main
.github/PULL_REQUEST_TEMPLATE.md	Rewritten with branch model guidance and updated checklist
docs/CONTRIBUTING.md	Full branch model diagram, commit convention guide, no-AI-files list
.gitignore	Added AI assistant config file patterns

Branch/ruleset protection (applied via API)

• main: require PR + 1 review + CODEOWNER review, require Trunk + Zsh + commit-lint checks, linear history, no force-push, no direct push, dismiss stale reviews
• next: require PR + 1 review, require Trunk + commit-lint checks, linear history, no force-push
• Repo settings: merge commits disabled (squash or rebase only), auto-delete branches on merge
• Rulesets: main — release gate and next — integration gate enforce conventional commit message pattern at the push layer

Commit guidelines enforced

type(scope): short description   ≤72 chars, imperative mood
Types: feat  fix  perf  refactor  docs  test  ci  chore  revert

No AI co-author trailers (Co-authored-by: Copilot, Co-authored-by: Claude, etc.) are blocked by the commit-lint workflow.

[Copilot]

Pull request overview

This PR adds repository governance/CI guardrails to enforce the branch model (next as integration), Conventional Commits, and a “no AI config files / no AI co-author trailers” policy.

Changes:

• Add a new commit-lint workflow to validate commit subjects, PR titles, branch names, and block AI co-author trailers.
• Expand Trunk CI to run on next branch pushes (in addition to main).
• Update contributor-facing docs/templates and .gitignore to document/enforce the branch/commit model and AI-file exclusions.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
docs/CONTRIBUTING.md	Rewrites contributing guidelines with branch model + Conventional Commits + “what not to add”.
.gitignore	Ignores common AI-assistant config files and restores .trunk/out* ignore entry formatting.
.github/workflows/trunk-check.yml	Runs Trunk checks on pushes to main and next.
.github/workflows/commit-lint.yml	Adds CI checks for Conventional Commits, PR title format, branch naming, and AI co-author trailers.
.github/PULL_REQUEST_TEMPLATE.md	Updates PR template to reflect branch/commit rules and contributor checklist.
.github/copilot-instructions.md	Adds Copilot-specific guidance aligned with the repo’s branch/commit/AIs policy.

Comments suppressed due to low confidence (1)

.github/workflows/commit-lint.yml:90

• Same issue as the commit subject check: this PR title regex limits only the text after : to 72 characters, not the full title length, but the repo guidance says the subject/title line must be ≤72 total. This will allow titles longer than intended.

        run: |
          PATTERN='^(feat|fix|perf|refactor|docs|test|ci|chore|revert)(\([^)]+\))?!?: .{1,72}$'
          if ! echo "$PR_TITLE" | grep -qE "$PATTERN"; then
            echo "❌ PR title does not follow Conventional Commits format."
            echo "   Got:      $PR_TITLE"
            echo "   Expected: type(scope): short description"
            echo "   Types:    feat, fix, perf, refactor, docs, test, ci, chore, revert"

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