fix: remove duplicate language selector container from mobile menu

The navbar had two language selector containers:
1. Main navbar: #language-selector-container (responsive design)
2. Mobile menu: #mobile-menu-language-selector (unused, empty)

Since the main navbar language selector already has responsive behavior:
- Desktop: Shows dropdown with text
- Mobile: Shows icon-only buttons

The mobile menu duplicate container is unnecessary and caused confusion.

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

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

public/js/components/navbar.js

@@ -71,9 +71,6 @@ class TractatusNavbar {
               </button>
             </div>
             <nav class="p-5 space-y-3">
-              <!-- Language Selector in Mobile Menu -->
-              <div id="mobile-menu-language-selector"></div>
-
               <div class="pb-3 mb-3 border-b border-gray-200">
                 <p class="text-xs font-semibold text-gray-500 uppercase tracking-wider mb-2 px-3">Audiences</p>
                 <a href="/researcher.html" class="block px-3 py-2.5 text-gray-700 hover:bg-blue-50 hover:text-blue-700 rounded-lg transition font-medium">