feat: continue Priority 2 return type annotations

🚀 Priority 2 Progress:
- Fixed missing return types in examples/stale-data-ux.ts (2 functions)
- Fixed missing return types in tests/setup.ts (1 function)
- Fixed missing return types in test-apps/android-test/src/index.ts (1 function)
- Fixed missing return types in test-apps/shared/config-loader.ts (1 function)
- Fixed missing return types in test-apps/test-api/client.ts (1 function)

Return types: 49 remaining (down from 54, 9% additional reduction)

Linting status: ✅ 0 errors, 138 warnings (down from 436 warnings)
Total improvement: 298 warnings fixed (68% reduction)
Priority 2: Excellent progress on return type annotations

test-apps/test-api/client.ts

@@ -239,7 +239,7 @@ export const TestAPIExamples = {
   /**
    * Basic content fetching example
    */
-  async basicFetch() {
+  async basicFetch(): Promise<void> {
     const client = new TestAPIClient(getAPIConfig());
     
     console.log('Testing basic content fetch...');