feat: OAuth user fixes + dashboard UI improvements (v3.2.0)

- Bug A: Fix OAuth consent redirect loop (return_url path-relative)
- Bug B: Accept OAuth JWT tokens on /u/{user_id}/{alias}/mcp
- Bug C: Add user OAuth client CRUD (list/create/delete) + new page
- D-1: Sidebar border via Tailwind class, version footer in sidebar
- D-2: Remove broken setInterval targeting #stats-container
- D-3: 404.html purple primary colors + system dark mode support
- D-4: Fix invisible buttons (bg-gray-200 + text-white in light mode)
- D-5: Pin Alpine.js to 3.14.8, remove duplicate CSRF meta tag
- D-6: Fix invisible lang toggle button in settings (dark mode)

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

core/templates/dashboard/settings/index.html

@@ -13,11 +13,11 @@
         <div class="space-y-4">
             <div class="flex items-center gap-4">
                 <a href="/dashboard/settings?lang=en"
-                   class="px-4 py-2 rounded-lg transition-colors {% if lang != 'fa' %}bg-primary-600 text-white{% else %}bg-gray-700 text-gray-700 dark:text-gray-300 hover:bg-gray-300 dark:hover:bg-gray-600{% endif %}">
+                   class="px-4 py-2 rounded-lg transition-colors {% if lang != 'fa' %}bg-primary-600 text-white{% else %}bg-gray-700 text-white dark:text-gray-300 hover:bg-gray-300 dark:hover:bg-gray-600{% endif %}">
                     English
                 </a>
                 <a href="/dashboard/settings?lang=fa"
-                   class="px-4 py-2 rounded-lg transition-colors {% if lang == 'fa' %}bg-primary-600 text-white{% else %}bg-gray-700 text-gray-700 dark:text-gray-300 hover:bg-gray-300 dark:hover:bg-gray-600{% endif %}">
+                   class="px-4 py-2 rounded-lg transition-colors {% if lang == 'fa' %}bg-primary-600 text-white{% else %}bg-gray-700 text-white dark:text-gray-300 hover:bg-gray-300 dark:hover:bg-gray-600{% endif %}">
                     فارسی
                 </a>
             </div>