feat: add Renovate stack sync workflow for automated stack regeneration

Author: wax911

.github/workflows/renovate-stack-sync.yml

@@ -0,0 +1,37 @@
+name: Renovate stack sync
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, ready_for_review]
+
+permissions:
+  contents: write
+
+jobs:
+  sync:
+    name: Regenerate stacks for Renovate PRs
+    if: github.actor == 'renovate[bot]' && github.event.pull_request.head.repo.full_name == github.repository
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Renovate branch
+        uses: actions/checkout@v6
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
+          fetch-depth: 0
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.x'
+
+      - name: Install Python deps
+        run: pip install -r tools/requirements.txt
+
+      - name: Regenerate stacks
+        run: python3 tools/generate_stacks.py
+
+      - name: Commit regenerated stacks when drift exists
+        uses: stefanzweifel/git-auto-commit-action@v5
+        with:
+          commit_message: "chore(stacks): sync generated stacks for renovate update"
+          file_pattern: stacks/*.yml