fix(hub): redirect Feishu OAuth default login to org admin SPA

Default returnTo=/admin previously landed on the static complete page
meant for chat onboarding; send users to /admin/org/:slug instead.

hub/src/admin/routes/authRoutes.ts

@@ -433,8 +433,10 @@ async function resolvePostLoginRedirect(
     });
     if (intended === null) return "/admin?error=not_an_active_org_member";
     const orgRoot = `/admin/org/${intended.organization.slug}`;
+    // Default / missing returnTo sanitizes to "/admin". Always land in the org
+    // admin SPA (not the legacy static "close this tab" complete page).
     if (returnTo === "/admin") {
-      return `/auth/feishu/complete?org=${encodeURIComponent(intended.organization.name)}`;
+      return orgRoot;
     }
     return returnTo === orgRoot || returnTo.startsWith(`${orgRoot}/`) ? returnTo : orgRoot;
   }