Update CI to push to Gitea container registry

- Login to gitea.voyager.sh registry
- Push on main branch, skip on PRs
- Tag with 'latest' and commit SHA

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -1,4 +1,4 @@
-name: Build Container
+name: Build and Push Container
 
 on:
   push:
@@ -10,6 +10,10 @@ on:
       - main
       - master
 
+env:
+  REGISTRY: gitea.voyager.sh
+  IMAGE_NAME: nick/kuma-strapper
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -20,11 +24,29 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      - name: Build Docker image
+      - name: Login to Gitea Container Registry
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.GITEA_TOKEN }}
+
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=raw,value=latest,enable=${{ github.ref == 'refs/heads/main' }}
+            type=sha,prefix=
+
+      - name: Build and push Docker image
         uses: docker/build-push-action@v5
         with:
           context: .
-          push: false
+          push: ${{ github.event_name != 'pull_request' }}
-          tags: kuma-strapper:${{ github.sha }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha,mode=max