fix(api-docs): Use absolute API URL for Interactive Explorer link

The Interactive Explorer link was using a relative URL (/v1/docs/), which caused it to open on the current subdomain instead of the API subdomain. This resulted in users being redirected to the dashboard.

Changed to use API_BASE_URL to construct the absolute URL, which will correctly point to:
- Local: http://lvh.me:8000/v1/docs/
- Production: https://api.smoothschedule.com/v1/docs/

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/pages/HelpApiDocs.tsx

@@ -12,6 +12,7 @@ import {
   AlertCircle,
 } from 'lucide-react';
 import { useTestTokensForDocs } from '../hooks/useApiTokens';
+import { API_BASE_URL } from '../api/config';
 
 // =============================================================================
 // TYPES & CONSTANTS
@@ -1111,7 +1112,7 @@ my $response = $ua->get('${SANDBOX_URL}/services/',
               )}
 
               <a
-                href="/v1/docs/"
+                href={`${API_BASE_URL}/v1/docs/`}
                 target="_blank"
                 rel="noopener noreferrer"
                 className="flex items-center gap-2 px-4 py-2 text-sm font-medium text-purple-600 dark:text-purple-400 hover:bg-purple-50 dark:hover:bg-purple-900/20 rounded-lg transition-colors"