ci: namespace registry images under repo owner

Gitea's OCI registry requires <host>/<owner>/<image>. Pushes to the
bare <host>/<image> path return 404. Prepend github.repository_owner
so REGISTRY_URL can stay as just the hostname.

.gitea/workflows/ci.yaml

@@ -104,9 +104,12 @@ jobs:
       - name: Log in to ${{ vars.REGISTRY_URL }}
         run: echo "${{ secrets.REGISTRY_TOKEN }}" | docker login "${{ vars.REGISTRY_URL }}" --username "${{ github.actor }}" --password-stdin
 
+      # Gitea's OCI registry is namespaced by owner — images must be at
+      # <host>/<owner>/<image>. Prepend the repo owner so REGISTRY_URL can
+      # stay as just the hostname.
       - name: Build & push API image
         run: |
-          IMAGE="${{ vars.REGISTRY_URL }}/vector-api"
+          IMAGE="${{ vars.REGISTRY_URL }}/${{ github.repository_owner }}/vector-api"
           docker build \
             -f apps/api/Dockerfile \
             -t "$IMAGE:${{ github.sha }}" \
@@ -117,7 +120,7 @@ jobs:
 
       - name: Build & push Web image
         run: |
-          IMAGE="${{ vars.REGISTRY_URL }}/vector-web"
+          IMAGE="${{ vars.REGISTRY_URL }}/${{ github.repository_owner }}/vector-web"
           docker build \
             -f apps/web/Dockerfile \
             -t "$IMAGE:${{ github.sha }}" \