Fix dashboard 404: derive API base from page path

Opening the dashboard at /crm (no trailing slash) made the relative `api/leads`
fetch resolve to /api/leads -> 404. Derive the API base from
location.pathname so it works at both /crm and /crm/.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backoffice/app/static/index.html

@@ -98,7 +98,10 @@
   </div>
 
   <script>
-    const API = 'api';
+    // Derive the API base from this page's own path so it works whether the
+    // dashboard is opened at /crm or /crm/ (relative fetches break without the
+    // trailing slash).
+    const API = location.pathname.replace(/\/+$/, '') + '/api';
     const TOKEN = '__CRM_TOKEN__';
     const COLS = {
       leads: ['lead_id','received_at','client_id','source','name','contact','service_interest','message','status','notified'],