fix(frontend): detect basePath from URL for config fetch

When running with basePath=/llm-admin, the fetch('/api/config') call
doesn't automatically prepend the basePath. Added detectBasePath()
function that checks window.location.pathname to determine the correct
API endpoint path.

Author: damienlaine

frontend/lib/config.ts

@@ -17,6 +17,21 @@ export interface ConfigContextValue extends RuntimeConfig {
 
 let cachedConfig: RuntimeConfig | null = null;
 
+/**
+ * Detects the basePath from the current URL.
+ * In production, the app runs at /llm-admin, so we detect this from the pathname.
+ */
+function detectBasePath(): string {
+  if (typeof window === 'undefined') return '';
+
+  // Check if we're running under a known basePath
+  const pathname = window.location.pathname;
+  if (pathname.startsWith('/llm-admin')) {
+    return '/llm-admin';
+  }
+  return '';
+}
+
 /**
  * Fetches runtime configuration from the API route.
  * Caches the result for subsequent calls within the same session.
@@ -27,7 +42,9 @@ export async function getConfig(): Promise<RuntimeConfig> {
   }
 
   try {
-    const response = await fetch('/api/config');
+    // Detect basePath from current URL and prepend to API route
+    const basePath = detectBasePath();
+    const response = await fetch(`${basePath}/api/config`);
     if (!response.ok) {
       throw new Error(`Config fetch failed: ${response.status}`);
     }