fix: derive registry host from gitea.server_url instead of unset variable

REGISTRY_URL var was empty so docker login fell through to Docker Hub.
Now strips protocol from gitea.server_url to get the registry hostname —
no manual variable needed. docker-compose defaults to the known host.

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

.gitea/workflows/deploy.yml

@@ -12,19 +12,23 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set image name
+      - name: Set image tags
         id: image
         run: |
-          IMAGE="${{ vars.REGISTRY_URL }}/josh/sixflagssupercalendar"
-          SHA="${{ github.sha }}"
-          echo "full=${IMAGE}" >> "$GITHUB_OUTPUT"
+          # 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: Log in to registry
         run: |
           echo "${{ secrets.REGISTRY_TOKEN }}" | \
-            docker login "${{ vars.REGISTRY_URL }}" -u josh --password-stdin
+            docker login "${{ steps.image.outputs.registry }}" -u josh --password-stdin
 
       - name: Build image
         run: |