fix: downgrade artifact actions to v3 for Gitea compatibility

- Changed upload-artifact from v4 to v3
- Changed download-artifact from v4 to v3
- Gitea Actions does not support artifact v4 API (GHES compatibility issue)

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

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

.gitea/workflows/deploy-synology.yml

@@ -125,7 +125,7 @@ jobs:
 
       - name: Upload Docker Image Artifact
         if: ${{ steps.validate.outputs.valid == 'true' }}
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: docker-image
           path: laravel-app.tar.gz
@@ -142,7 +142,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Download Docker Image Artifact
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v3
         with:
           name: docker-image