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

static/js/app.js

@@ -211,11 +211,11 @@ function setupUserMenu() {
         });
     }
     
-    // Profile button — shows user info modal
+    // Profile button — navigates to profile page
     if (profileBtn) {
         profileBtn.addEventListener('click', () => {
             wrapper.classList.remove('open');
-            showUserProfileModal();
+            window.location.href = '/profile.html';
         });
     }