Add optional CDK synth support to Python CI workflow

Enables Python CDK repos (po-ingest, workorder-ingest) to use the
same reusable workflow. Adds run-cdk-synth, cdk-dir, and node-version
inputs. Refactors dependency install to be shared between pytest and
cdk synth paths.

.github/workflows/ci-python-sam.yaml

@@ -23,6 +23,18 @@ on:
         description: "Path to SAM template file"
         type: string
         default: "template.yaml"
+      run-cdk-synth:
+        description: "Run cdk synth (for Python CDK repos)"
+        type: boolean
+        default: false
+      cdk-dir:
+        description: "Directory containing cdk.json"
+        type: string
+        default: "cdk"
+      node-version:
+        description: "Node.js version for CDK CLI"
+        type: string
+        default: "22"
 
 jobs:
   ci:
@@ -44,10 +56,12 @@ jobs:
       - name: Ruff format check
         run: ruff format --check ${{ inputs.source-dirs }}
 
-      - name: Install test dependencies
-        if: ${{ inputs.run-tests }}
+      - name: Install Python dependencies
+        if: ${{ inputs.run-tests || inputs.run-cdk-synth }}
         run: |
-          pip install pytest
+          if [ "${{ inputs.run-tests }}" = "true" ]; then
+            pip install pytest
+          fi
           for req in $(find . -name requirements.txt -not -path './.aws-sam/*'); do
             pip install -r "$req"
           done
@@ -56,6 +70,17 @@ jobs:
         if: ${{ inputs.run-tests }}
         run: pytest
 
+      - name: Setup Node.js
+        if: ${{ inputs.run-cdk-synth }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: ${{ inputs.node-version }}
+
+      - name: CDK synth
+        if: ${{ inputs.run-cdk-synth }}
+        working-directory: ${{ inputs.cdk-dir }}
+        run: npx -y cdk synth --quiet
+
       - name: Setup SAM CLI
         if: ${{ inputs.run-sam-validate }}
         uses: aws-actions/setup-sam@v2