chore(ci): add mindmodel validator workflow

.github/workflows/mindmodel-validate.yml

@@ -0,0 +1,39 @@
+name: mindmodel validate
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  schedule:
+    - cron: '0 4 * * 0' # weekly
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt || true
+
+      - name: Run tests
+        run: |
+          python -m pytest -q
+
+      - name: Run mindmodel validator if manifest exists
+        if: ${{ always() }}
+        run: |
+          if [ -f .mindmodel/manifest.yaml ]; then
+            python -m scripts.mindmodel.cli || true
+          else
+            echo "No .mindmodel/manifest.yaml present — skipping validator"
+          fi