Fix checkout token: use REGISTRY_TOKEN (GITEA_ prefix reserved)

Gitea reserves the GITEA_ prefix for secrets. Reuse the existing
REGISTRY_TOKEN PAT which already has repo read access.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -13,7 +13,7 @@ jobs:
       - name: Checkout
         uses: https://github.com/actions/checkout@v4
         with:
-          token: ${{ secrets.GITEA_TOKEN }}
+          token: ${{ secrets.REGISTRY_TOKEN }}
 
       - name: Login to Gitea Container Registry
         uses: https://github.com/docker/login-action@v3