ci: use docker/metadata-action and build-push-action

Cleaner pipeline using official Docker actions. Supports semver tags
alongside latest. Registry driven by vars.REGISTRY variable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -4,40 +4,37 @@ on:
   push:
     branches:
       - main
+    tags:
+      - 'v*'
 
 jobs:
-  build-and-push:
+  build-push:
+    name: Build & Push
     runs-on: ubuntu-latest
+    if: github.event_name == 'push'
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
+      - uses: actions/checkout@v4
 
-      - name: Set image tags
-        id: image
-        run: |
-          # Gitea's container registry lives on the same host as the Gitea instance
-          REGISTRY="${{ gitea.server_url }}"
-          REGISTRY="${REGISTRY#https://}"
-          REGISTRY="${REGISTRY#http://}"
-          IMAGE="${REGISTRY}/josh/sixflagssupercalendar"
-          SHA="${{ gitea.sha }}"
-          echo "registry=${REGISTRY}" >> "$GITHUB_OUTPUT"
-          echo "tag_latest=${IMAGE}:latest" >> "$GITHUB_OUTPUT"
-          echo "tag_sha=${IMAGE}:${SHA::8}" >> "$GITHUB_OUTPUT"
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ vars.REGISTRY }}/${{ gitea.repository_owner }}/sixflagssupercalendar
+          tags: |
+            type=semver,pattern={{version}}
+            type=raw,value=latest,enable={{is_default_branch}}
 
-      - name: Log in to registry
-        run: |
-          echo "${{ secrets.REGISTRY_TOKEN }}" | \
-            docker login "${{ steps.image.outputs.registry }}" -u josh --password-stdin
+      - name: Log in to Gitea registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ vars.REGISTRY }}
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.REGISTRY_TOKEN }}
 
-      - name: Build image
-        run: |
-          docker build \
-            -t "${{ steps.image.outputs.tag_latest }}" \
-            -t "${{ steps.image.outputs.tag_sha }}" \
-            .
-
-      - name: Push image
-        run: |
-          docker push "${{ steps.image.outputs.tag_latest }}"
-          docker push "${{ steps.image.outputs.tag_sha }}"
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}