refactor: use Gitea container registry instead of Docker Hub

Image will be pushed to: code.letsbe.solutions/letsbe/sysadmin-agent

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitea/workflows/build.yml

@@ -13,8 +13,8 @@ on:
       - master
 
 env:
-  REGISTRY: docker.io
-  IMAGE_NAME: letsbesolutions/sysadmin-agent
+  REGISTRY: code.letsbe.solutions
+  IMAGE_NAME: letsbe/sysadmin-agent
 
 jobs:
   build:
@@ -26,12 +26,13 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      - name: Log in to Docker Hub
+      - name: Log in to Gitea Container Registry
         if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
         with:
-          username: ${{ secrets.DOCKER_USERNAME }}
-          password: ${{ secrets.DOCKER_TOKEN }}
+          registry: ${{ env.REGISTRY }}
+          username: ${{ gitea.actor }}
+          password: ${{ secrets.GITEA_TOKEN }}
 
       - name: Extract metadata (tags, labels)
         id: meta