feat: redesign admin panel & profile page, optimize Dockerfile, remove rootless

- Completely redesign admin.html matching OxiCloud design system
- Create standalone profile.html page with avatar, details & password change
- Optimize Dockerfile: 3-stage build, non-root user, OCI labels, layer cache
- Add .dockerignore to reduce build context
- Remove redundant Dockerfile.rootless & rootless-compose.yml
- Redesign login language selector as compact dropdown with search
- Fix CI/CD workflows (ci.yml, docker-build.yml, docker-publish.yml)
- Update app.js to navigate to profile page instead of modal

.github/workflows/docker-build.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
@@ -30,7 +30,7 @@ jobs:
             type=sha
 
       - name: Build Docker image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           push: false