Migrate workflow from .github to .gitea/workflows

Switch registry from ghcr.io to git.necloud.us and update secrets
to REGISTRY_USER / REGISTRY_TOKEN for Gitea Actions compatibility.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/docker.yml

@@ -8,24 +8,21 @@ on:
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
-    permissions:
-      contents: read
-      packages: write
 
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Log in to GitHub Container Registry
+      - name: Log in to Gitea Container Registry
         uses: docker/login-action@v3
         with:
-          registry: ghcr.io
+          registry: git.necloud.us
-          username: ${{ github.actor }}
+          username: ${{ secrets.REGISTRY_USER }}
-          password: ${{ secrets.GITHUB_TOKEN }}
+          password: ${{ secrets.REGISTRY_TOKEN }}
 
       - name: Build and push
         uses: docker/build-push-action@v6
         with:
           context: .
           push: true
-          tags: ghcr.io/nmemmert/spelling:latest
+          tags: git.necloud.us/nate/homeschool:latest