fix: backend url normalization

src/config/instances.ts

@@ -29,8 +29,13 @@ const ACTIVE_KEY = 'mcma:activeInstance';
 const LEGACY_URL_KEY = 'mcma_api_base_url';
 const LEGACY_AUTH_KEY = 'mcma_auth';
 
+// The UI always talks to the `/api/v1` contract, so users only enter the
+// origin (and optional reverse-proxy prefix). We append the contract path
+// here, the single choke point for both the base URL and the instance id, so
+// `domain.com`, `domain.com/`, and `domain.com/api/v1` all converge.
 function normalizeUrl(url: string): string {
-  return url.trim().replace(/\/+$/, '');
+  const trimmed = url.trim().replace(/\/+$/, '');
+  return /\/api\/v1$/.test(trimmed) ? trimmed : `${trimmed}/api/v1`;
 }
 
 /** Stable, readable id from a base URL — also serves as the storage namespace. */