Replace actions/checkout with manual git clone

The docker:dind image doesn't include Node.js which is required
by actions/checkout@v4. Use manual git commands instead.

Changes:
- Install git via apk (Alpine package manager)
- Clone repository directly
- Checkout specific commit SHA

This approach works with docker:dind's minimal Alpine base.

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

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

.gitea/workflows/build-deploy.yml

@@ -14,7 +14,10 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        run: |
+          apk add --no-cache git
+          git clone https://code.puffinoffset.com/matt/puffin-app.git .
+          git checkout ${{ github.sha }}
 
       - name: Log in to Gitea Container Registry
         run: |