refactor: move distributed files to src/, add sync check CI

- Distributed files now live in src/ — consumers use `path: src/`
- Top-level files are identical copies (repo eats its own dog food)
- CI sync-check job validates top-level and src/ stay in sync
- Removed .common-repo.yaml (path: scoping replaces source excludes)
- Updated README with new structure and usage

.github/workflows/ci.yaml

@@ -0,0 +1,44 @@
+name: CI
+
+on:
+  workflow_call:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  sync-check:
+    name: Verify src/ sync
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5
+      - name: Check top-level files match src/
+        run: |
+          # Verify distributed files in src/ match the repo's own copies
+          status=0
+          for file in .releaserc.yaml commitlint.config.js; do
+            if ! diff -q "$file" "src/$file" > /dev/null 2>&1; then
+              echo "❌ $file differs from src/$file"
+              diff --color "$file" "src/$file" || true
+              status=1
+            else
+              echo "✅ $file matches src/$file"
+            fi
+          done
+          for file in .github/workflows/commitlint.yml .github/workflows/release.yaml; do
+            if ! diff -q "$file" "src/$file" > /dev/null 2>&1; then
+              echo "❌ $file differs from src/$file"
+              diff --color "$file" "src/$file" || true
+              status=1
+            else
+              echo "✅ $file matches src/$file"
+            fi
+          done
+          if [ $status -ne 0 ]; then
+            echo ""
+            echo "Top-level files and src/ are out of sync."
+            echo "Copy changes to both locations, or run: cp .releaserc.yaml commitlint.config.js src/ && cp .github/workflows/commitlint.yml .github/workflows/release.yaml src/.github/workflows/"
+            exit 1
+          fi
+          echo ""
+          echo "All distributed files in sync ✅"