fix(marketplace): resolve app detail page routing and styling issues

- Fixed JavaScript errors from missing HTML elements (install-code, usage-code, integration-code)
- Added missing CSS classes for tabs, overview layout, sidebar, and integration content
- Fixed tab navigation to display horizontally in single line
- Added proper padding to tab content sections (removed from container, added to content)
- Fixed tab selector from .nav-tab to .tab-btn to match HTML structure
- Added sidebar styling with stats grid and metadata display
- Improved responsive design with mobile-friendly tab scrolling
- Fixed code block positioning for copy buttons
- Removed margin from first headings to prevent extra spacing
- Added null checks for DOM elements in JavaScript to prevent errors

These changes resolve the routing issue where clicking on apps caused page redirects,
and fix the broken layout where CSS was not properly applied to the app detail page.

docs/md_v2/marketplace/frontend/app-detail.js

@@ -1,5 +1,15 @@
 // App Detail Page JavaScript
-const API_BASE = '/marketplace/api';
+const { API_BASE, API_ORIGIN } = (() => {
+    const { hostname, port, protocol } = window.location;
+    const isLocalHost = ['localhost', '127.0.0.1', '0.0.0.0'].includes(hostname);
+
+    if (isLocalHost && port && port !== '8100') {
+        const origin = `${protocol}//127.0.0.1:8100`;
+        return { API_BASE: `${origin}/marketplace/api`, API_ORIGIN: origin };
+    }
+
+    return { API_BASE: '/marketplace/api', API_ORIGIN: '' };
+})();
 
 class AppDetailPage {
     constructor() {