ci: add conventional commit format check (#399)

## Summary
- Add `conventional-commit` CI job that validates PR titles and push
commit messages follow the `type(scope)?: description` format
- Valid types: `feat`, `fix`, `refactor`, `chore`, `build`, `ci`,
`docs`, `test`, `perf`, `style`, `revert`
- Runs on both PR and push events, skips tag pushes
- Zero dependencies, pure bash regex check

## Test plan
- [x] PR title of this PR itself passes the check
- [ ] CI runs and passes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Enhanced continuous integration pipeline to validate commit message
formatting standards on all pull requests and commits.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/main.yml

@@ -47,6 +47,31 @@ jobs:
               - 'config/**'
               - '.github/workflows/test-cmake.yml'
 
+  conventional-commit:
+    if: ${{ !startsWith(github.ref, 'refs/tags/') }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check conventional commit format
+        env:
+          IS_PR: ${{ github.event_name == 'pull_request' }}
+          PR_TITLE: ${{ github.event.pull_request.title }}
+          COMMIT_MSG: ${{ github.event.head_commit.message }}
+        run: |
+          pattern='^(feat|fix|refactor|chore|build|ci|docs|test|perf|style|revert)(\(.+\))?: .+'
+          if [[ "$IS_PR" == "true" ]]; then
+            subject="$PR_TITLE"
+            label="PR title"
+          else
+            subject=$(echo "$COMMIT_MSG" | head -n1)
+            label="Commit message"
+          fi
+          if [[ ! "$subject" =~ $pattern ]]; then
+            echo "::error::$label must follow conventional commit format: type(scope)?: description"
+            echo "  Valid types: feat, fix, refactor, chore, build, ci, docs, test, perf, style, revert"
+            echo "  Got: '$subject'"
+            exit 1
+          fi
+
   format:
     needs: changes
     if: ${{ needs.changes.outputs.format == 'true' }}
@@ -92,6 +117,7 @@ jobs:
   checks-passed:
     if: ${{ always() && !startsWith(github.ref, 'refs/tags/') }}
     needs:
+      - conventional-commit
       - format
       - deploy
       # - clice
@@ -103,5 +129,5 @@ jobs:
       - name: Check results
         uses: re-actors/alls-green@release/v1
         with:
-          allowed-skips: format,deploy,clice,vscode,cmake
+          allowed-skips: conventional-commit,format,deploy,clice,vscode,cmake
           jobs: ${{ toJSON(needs) }}