Strip scheme from REGISTRY_URL before tagging

Docker image tags must start with a hostname — a `https://` prefix in
the REGISTRY_URL variable produced `invalid reference format`. Normalize
the value in a prep step (drop http/https scheme and trailing slash) so
the workflow works whether the variable is set as a URL or a bare host.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-push.yml

@@ -14,9 +14,15 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Compute short SHA
+      - name: Prepare build vars
         id: vars
-        run: echo "sha_short=${GITHUB_SHA::7}" >> "$GITHUB_OUTPUT"
+        run: |
+          host="${{ vars.REGISTRY_URL }}"
+          host="${host#https://}"
+          host="${host#http://}"
+          host="${host%/}"
+          echo "registry=$host" >> "$GITHUB_OUTPUT"
+          echo "sha_short=${GITHUB_SHA::7}" >> "$GITHUB_OUTPUT"
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
@@ -24,7 +30,7 @@ jobs:
       - name: Login to Gitea registry
         uses: docker/login-action@v3
         with:
-          registry: ${{ vars.REGISTRY_URL }}
+          registry: ${{ steps.vars.outputs.registry }}
           username: ${{ gitea.actor }}
           password: ${{ secrets.REGISTRY_TOKEN }}
 
@@ -34,5 +40,5 @@ jobs:
           context: .
           push: true
           tags: |
-            ${{ vars.REGISTRY_URL }}/${{ env.IMAGE }}:latest
-            ${{ vars.REGISTRY_URL }}/${{ env.IMAGE }}:sha-${{ steps.vars.outputs.sha_short }}
+            ${{ steps.vars.outputs.registry }}/${{ env.IMAGE }}:latest
+            ${{ steps.vars.outputs.registry }}/${{ env.IMAGE }}:sha-${{ steps.vars.outputs.sha_short }}