feat(login): add plugin seam for default landing path

Plugins can supply `LoginPlugin.resolveDefaultPath` to override the
post-login redirect target. checkDefaultPage consults the hook and
uses the returned path when non-null; otherwise falls back to the
existing admin/non-admin defaults. The lookup runs in parallel with
the IS_FIRST_LOGIN read. Applies to both first-login and
subsequent-login flows.

src/plugins/types.ts

@@ -48,6 +48,15 @@ export interface LoginKit {
 export interface LoginPlugin {
   shouldUseCustomLogin?: (enterpriseSettings: any) => boolean;
   CustomLoginComponent?: ComponentType<{ kit: LoginKit }>;
+  /**
+   * Seam for plugins to override the default landing path after login.
+   * Returning a path overrides both the admin and non-admin defaults;
+   * returning null/undefined falls back to the built-in behavior.
+   */
+  resolveDefaultPath?: (
+    userInfo: any,
+    ctx: { request: <T = any>(url: string, options?: any) => Promise<T> }
+  ) => Promise<string | null | undefined> | string | null | undefined;
 }
 
 /**