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/index.html

@@ -444,12 +444,4 @@
 {% endblock %}
 
 {% block scripts %}
-<script>
-    // Auto-refresh dashboard every 30 seconds
-    htmx.config.defaultSwapStyle = 'outerHTML';
-
-    setInterval(function() {
-        htmx.ajax('GET', '/api/dashboard/stats', {target: '#stats-container', swap: 'none'});
-    }, 30000);
-</script>
 {% endblock %}