feat: support optional per-installation Basic Auth on the MCP proxy

Lets a client still using Basic Auth credentials (e.g. against the
previous nginx + htpasswd setup) keep working without switching to a
bearer token immediately. Bearer auth remains the default and the
only option when no Basic Auth credentials are configured.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/server/src/service/orchestrator.ts

@@ -53,6 +53,8 @@ export function configureInstallation(
     hostEnvVar?: string;
     httpPath?: string;
     internalPort?: number;
+    basicAuthUsername?: string | null;
+    basicAuthPassword?: string | null;
   },
 ): Installation {
   return updateInstallation(id, patch);