REFACTOR(auth): use gitea secret

- Use Gitea-provided secret for registry authentication
- Simplify credential management

.gitea/workflows/build.yml

@@ -29,7 +29,7 @@ jobs:
 
       - name: Log in to Gitea Container Registry
         run: |
-          echo "${{ secrets.GITEA_PACKAGE_TOKEN }}" | docker login ${{ env.REGISTRY }} -u bluemayne --password-stdin
+          echo "${{ secrets.GITEA }}" | docker login ${{ env.REGISTRY }} -u bluemayne --password-stdin
 
       - name: Lowercase repository name
         id: lowercase