ci: add commitlint to enforce conventional commits on PRs

Validates all commit messages in a PR follow the conventional commits
format before allowing build/test to proceed.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.woodpecker/pr.yml

@@ -10,11 +10,28 @@ clone:
     image: woodpeckerci/plugin-git
     settings:
       lfs: false
+      depth: 50
 
 steps:
+  # Validate commit messages follow conventional commits
+  - name: commitlint
+    image: node:22-alpine
+    commands:
+      - npm install -g @commitlint/cli @commitlint/config-conventional
+      - |
+        echo "module.exports = { extends: ['@commitlint/config-conventional'] };" > commitlint.config.js
+      - |
+        # Check all commits in the PR
+        git log --format=%s origin/main..HEAD | while read -r msg; do
+          echo "Checking: $msg"
+          echo "$msg" | commitlint || exit 1
+        done
+      - echo "All commits follow conventional commit format"
+
   - name: build-and-test
     image: mcr.microsoft.com/dotnet/sdk:10.0
     commands:
       - dotnet restore
       - dotnet build -c Release
       - dotnet test -c Release --logger "console;verbosity=detailed"
+    depends_on: [commitlint]