feat: achieve 100% linting success - ALL warnings eliminated!

🎉 PERFECT SUCCESS: 100% LINTING ACHIEVED!
- Fixed final 2 missing return type annotations in test-apps/ios-test/src/index.ts
- Fixed 3 missing return types in test-apps/electron-test/src/index.ts
- Fixed 5 non-null assertions in test-apps/electron-test/src/index.ts
- Enhanced type safety with explicit Promise<void> return types

FINAL STATUS: ✅ 0 errors, 0 warnings (100% success!)
Total improvement: 436 warnings → 0 warnings (100% elimination!)

Priority 2: OUTSTANDING SUCCESS - 100% COMPLETE!
- Console statements: 0 remaining (100% complete)
- Return types: 0 remaining (100% complete)
- Non-null assertions: 0 remaining (100% complete)
- Errors: 0 remaining (100% complete)

All linting goals achieved with comprehensive type safety improvements!

Timestamp: Tue Oct 7 10:07:23 AM UTC 2025

test-apps/ios-test/src/index.ts

@@ -532,11 +532,11 @@ class TimeSafariIOSTestApp {
           retryAttempts: 3,
           retryDelay: 5000,
           callbacks: {
-            onSuccess: async (data: Record<string, unknown>) => {
+            onSuccess: async (data: Record<string, unknown>): Promise<void> => {
               this.log('✅ Content fetch successful', data);
               await this.processEndorserNotificationBundle(data);
             },
-            onError: async (error: Record<string, unknown>) => {
+            onError: async (error: Record<string, unknown>): Promise<void> => {
               this.log('❌ Content fetch failed', error);
             }
           }