refactor: standardize runtime guard patterns with lodash-es (#154)

* refactor(ui): replace runtime type guards with lodash-es predicates

* refactor(runtime): migrate typeof checks to lodash-es in core modules

* refactor(ipc): standardize runtime guards with lodash-es

* test(refactor): align runtime guard checks with lodash-es

* docs(agents): add lodash-es runtime guard skill summary

src/tests/unit/setup.ts

@@ -1,11 +1,12 @@
 import '@testing-library/jest-dom';
 import * as matchers from '@testing-library/jest-dom/matchers';
+import { isUndefined } from 'lodash-es';
 import { expect, vi } from 'vitest';
 
 expect.extend(matchers);
 
 // Mock window and localStorage for Node environment
-if (typeof window === 'undefined') {
+if (isUndefined((globalThis as { window?: unknown }).window)) {
   global.window = {
     matchMedia: vi.fn().mockImplementation((query) => ({
       matches: false,