ci(release): use REGISTRY_TOKEN PAT for Gitea registry login

The auto-provisioned GITHUB_TOKEN in Gitea Actions does not carry
package-registry write permission. Use a personal access token stored
as a repo secret instead.

.github/workflows/release-image.yml

@@ -46,7 +46,7 @@ jobs:
         # GITHUB_TOKEN is auto-provisioned by Gitea Actions for the running
         # workflow; no manual secret configuration required.
         run: |
-          echo "${{ secrets.GITHUB_TOKEN }}" | \
+          echo "${{ secrets.REGISTRY_TOKEN }}" | \
             docker login "${{ steps.registry.outputs.host }}" \
               -u "${{ github.actor }}" --password-stdin