ci: add worker validation and Docker build checks

Add automated validation to prevent worker-related issues:

**Worker Validation Script:**
- New script: .github/scripts/validate-workers.sh
- Validates all workers in docker-compose.yml exist
- Checks required files: Dockerfile, requirements.txt, worker.py
- Verifies files are tracked by git (not gitignored)
- Detects gitignore issues that could hide workers

**CI Workflow Updates:**
- Added validate-workers job (runs on every PR)
- Added build-workers job (runs if workers/ modified)
- Uses Docker Buildx for caching
- Validates Docker images build successfully
- Updated test-summary to check validation results

**PR Template:**
- New pull request template with comprehensive checklist
- Specific section for worker-related changes
- Reminds contributors to validate worker files
- Includes documentation and changelog reminders

These checks would have caught the secrets worker gitignore issue.

Implements Phase 1 improvements from CI/CD quality assessment.

.github/workflows/test.yml

@@ -7,6 +7,36 @@ on:
     branches: [ main, master, develop ]
 
 jobs:
+  validate-workers:
+    name: Validate Workers
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Run worker validation
+        run: |
+          chmod +x .github/scripts/validate-workers.sh
+          .github/scripts/validate-workers.sh
+
+  build-workers:
+    name: Build Worker Docker Images
+    runs-on: ubuntu-latest
+    # Only run if workers directory is modified
+    if: |
+      github.event_name == 'pull_request' &&
+      contains(github.event.pull_request.changed_files, 'workers/')
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Build worker images
+        run: |
+          echo "Building worker Docker images..."
+          docker compose build worker-python worker-secrets worker-rust worker-android worker-ossfuzz --no-cache
+        continue-on-error: false
+
   lint:
     name: Lint
     runs-on: ubuntu-latest
@@ -143,11 +173,15 @@ jobs:
   test-summary:
     name: Test Summary
     runs-on: ubuntu-latest
-    needs: [lint, unit-tests]
+    needs: [validate-workers, lint, unit-tests]
     if: always()
     steps:
       - name: Check test results
         run: |
+          if [ "${{ needs.validate-workers.result }}" != "success" ]; then
+            echo "Worker validation failed"
+            exit 1
+          fi
           if [ "${{ needs.unit-tests.result }}" != "success" ]; then
             echo "Unit tests failed"
             exit 1