fix: Separate Docker workflows for testing and publishing

- Add docker-test.yml for PR validation (build test only)
- Fix build_and_publish_docker.yml to trigger only on tags
- Remove problematic sha prefix causing invalid tag format
- Ensure proper workflow sequence: PR test → merge → version → publish

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/docker-test.yml

@@ -0,0 +1,31 @@
+name: Docker Build Test
+
+on:
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  docker-build-test:
+    runs-on: ubuntu-latest
+    
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v4
+
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v3
+
+    - name: Test Docker build
+      uses: docker/build-push-action@v5
+      with:
+        context: .
+        push: false
+        tags: test:latest
+        cache-from: type=gha
+        cache-to: type=gha,mode=max
+
+    - name: Build test summary
+      run: |
+        echo "### ✅ Docker Build Test Passed" >> $GITHUB_STEP_SUMMARY
+        echo "" >> $GITHUB_STEP_SUMMARY
+        echo "Docker image builds successfully and is ready for production." >> $GITHUB_STEP_SUMMARY