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/electron-test/src/index.ts

@@ -284,13 +284,23 @@ class TimeSafariElectronTestApp {
     this.timeSafariNotificationManager = new TimeSafariNotificationManager();
     
     // Initialize UI components
+    const permissionStatusContainer = document.getElementById('permission-status-container');
+    const permissionDialogContainer = document.getElementById('permission-dialog-container');
+    const settingsContainer = document.getElementById('settings-container');
+    const statusContainer = document.getElementById('status-container');
+    const errorContainer = document.getElementById('error-container');
+    
+    if (!permissionStatusContainer || !permissionDialogContainer || !settingsContainer || !statusContainer || !errorContainer) {
+      throw new Error('Required UI containers not found');
+    }
+    
     this.permissionManager = new PermissionManager(
-      document.getElementById('permission-status-container')!,
-      document.getElementById('permission-dialog-container')!
+      permissionStatusContainer,
+      permissionDialogContainer
     );
-    this.settingsPanel = new SettingsPanel(document.getElementById('settings-container')!);
-    this.statusDashboard = new StatusDashboard(document.getElementById('status-container')!);
-    this.errorDisplay = new ErrorDisplay(document.getElementById('error-container')!);
+    this.settingsPanel = new SettingsPanel(settingsContainer);
+    this.statusDashboard = new StatusDashboard(statusContainer);
+    this.errorDisplay = new ErrorDisplay(errorContainer);
     
     this.setupEventListeners();
     this.initializeUI();
@@ -298,7 +308,7 @@ class TimeSafariElectronTestApp {
     this.log('TimeSafari Electron Test app initialized with Phase 4 components');
   }
 
-  private setupEventListeners() {
+  private setupEventListeners(): void {
     // Original test functionality
     document.getElementById('configure')?.addEventListener('click', () => this.testConfigure());
     document.getElementById('schedule')?.addEventListener('click', () => this.testSchedule());
@@ -466,7 +476,7 @@ class TimeSafariElectronTestApp {
     }
   }
 
-  private async testConfigure() {
+  private async testConfigure(): Promise<void> {
     try {
       this.log('Testing TimeSafari Electron configuration...');
       await this.configLoader.loadConfig();
@@ -646,7 +656,7 @@ class TimeSafariElectronTestApp {
     }
   }
 
-  private async testPerformance() {
+  private async testPerformance(): Promise<void> {
     try {
       this.log('Testing Electron performance metrics...');
       const metrics = {

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);
             }
           }