Switch to Docker-based workflow with CLI commands

Replace Kaniko approach with direct Docker CLI commands.
The Gitea runner mounts Docker socket, making Docker available
in ubuntu-latest environment.

Key changes:
- Remove container specification (Kaniko lacks shell utilities)
- Use docker login with password-stdin for authentication
- Build with docker build using multiple -t tags
- Push both latest and commit SHA tags
- Works with Docker-based Gitea runners

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

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

.gitea/workflows/build-deploy.yml

@@ -8,24 +8,26 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
-    container:
-      image: gcr.io/kaniko-project/executor:debug
 
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
 
-      - name: Prepare Kaniko config
+      - name: Log in to Gitea Container Registry
         run: |
-          mkdir -p /kaniko/.docker
-          echo "{\"auths\":{\"code.puffinoffset.com\":{\"auth\":\"$(echo -n "${{ github.actor }}:${{ secrets.GITHUB_TOKEN }}" | base64)\"}}}" > /kaniko/.docker/config.json
+          echo "${{ secrets.GITHUB_TOKEN }}" | docker login code.puffinoffset.com -u ${{ github.actor }} --password-stdin
 
-      - name: Build and push with Kaniko
+      - name: Build Docker image
         run: |
-          /kaniko/executor \
-            --context=${{ github.workspace }} \
-            --dockerfile=${{ github.workspace }}/Dockerfile \
-            --destination=code.puffinoffset.com/matt/puffin-app:latest \
-            --destination=code.puffinoffset.com/matt/puffin-app:main-${{ github.sha }} \
-            --cache=true \
-            --cache-repo=code.puffinoffset.com/matt/puffin-app/cache
+          docker build -t code.puffinoffset.com/matt/puffin-app:latest \
+                       -t code.puffinoffset.com/matt/puffin-app:main-${{ github.sha }} \
+                       .
+
+      - name: Push Docker images
+        run: |
+          docker push code.puffinoffset.com/matt/puffin-app:latest
+          docker push code.puffinoffset.com/matt/puffin-app:main-${{ github.sha }}
+
+      - name: Show image info
+        run: |
+          docker images | grep puffin-app