fix(marketplace): Update URLs to use /marketplace path and relative API endpoints

- Change API_BASE to relative '/api' for production
- Move marketplace to /marketplace instead of /marketplace/frontend
- Update MkDocs navigation
- Fix logo path in marketplace index

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

@@ -1,5 +1,5 @@
 // App Detail Page JavaScript
-const API_BASE = 'http://localhost:8100/api';
+const API_BASE = '/api';
 
 class AppDetailPage {
     constructor() {

docs/md_v2/marketplace/frontend/marketplace.js

@@ -1,5 +1,5 @@
 // Marketplace JS - Magazine Layout
-const API_BASE = 'http://localhost:8100/api';
+const API_BASE = '/api';
 const CACHE_TTL = 3600000; // 1 hour in ms
 
 class MarketplaceCache {