ci: add conventional commit validation to CI pipeline (#24)

* ci: add conventional commit validation to CI pipeline

Add a new CI job that validates all commits in pull requests follow
Conventional Commits format. This ensures compatibility with release-please
and prevents releases from failing due to unparseable commit messages.

The validator checks for:
- Standard types (feat, fix, docs, style, refactor, perf, test, build, ci, chore, revert)
- Optional scope in parentheses
- Optional breaking change indicator (!)
- Proper format: type(scope)!: description

Additionally validates PR titles using action-semantic-pull-request.

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

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: skip merge commits in conventional commit validation

GitHub automatically creates merge commits for PR branches that don't
follow conventional commit format. These should be skipped during
validation as they're automatically generated and don't affect
release-please's parsing of actual commits.

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

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: bokelley

.github/workflows/ci.yml

@@ -39,6 +39,56 @@ jobs:
         run: |
           pytest tests/ -v --cov=src/adcp --cov-report=term-missing
 
+  conventional-commits:
+    name: Validate conventional commit format
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Validate PR commits
+        uses: amannn/action-semantic-pull-request@v5
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Validate individual commits
+        run: |
+          # Get the base branch
+          BASE_SHA=$(git merge-base origin/${{ github.base_ref }} HEAD)
+
+          # Check each commit since the base
+          echo "Validating commits since $BASE_SHA..."
+          git log --format="%H %s" $BASE_SHA..HEAD | while read sha message; do
+            # Skip merge commits (GitHub automatically creates these)
+            if echo "$message" | grep -qE '^Merge [0-9a-f]+ into [0-9a-f]+'; then
+              echo "⊙ Skipping merge commit: $sha"
+              continue
+            fi
+
+            # Check if message matches conventional commit format
+            if ! echo "$message" | grep -qE '^(feat|fix|docs|style|refactor|perf|test|build|ci|chore|revert)(\([^)]+\))?!?: .+'; then
+              echo "❌ Commit $sha does not follow Conventional Commits format:"
+              echo "   $message"
+              echo ""
+              echo "Expected format: <type>[optional scope]: <description>"
+              echo "Types: feat, fix, docs, style, refactor, perf, test, build, ci, chore, revert"
+              echo ""
+              echo "Examples:"
+              echo "  feat: add new feature"
+              echo "  fix: resolve bug in parser"
+              echo "  feat(api): add new endpoint"
+              echo "  feat!: breaking change"
+              exit 1
+            else
+              echo "✓ $sha: $message"
+            fi
+          done
+          echo ""
+          echo "✅ All commits follow Conventional Commits format"
+
   schema-check:
     name: Validate schemas are up-to-date
     runs-on: ubuntu-latest