Made app default to system-defined dark/light mode on first launch

Session/Meta/AppDelegate.m

@@ -194,7 +194,7 @@ static NSTimeInterval launchStartedAt;
     mainWindow.rootViewController = [LoadingViewController new];
     [mainWindow makeKeyAndVisible];
 
-    LKAppMode appMode = [NSUserDefaults.standardUserDefaults integerForKey:@"appMode"];
+    LKAppMode appMode = [self getAppModeOrSystemDefault];
     [self setCurrentAppMode:appMode];
 
     if (@available(iOS 11, *)) {
@@ -245,7 +245,7 @@ static NSTimeInterval launchStartedAt;
 
     [self ensureRootViewController];
 
-    LKAppMode appMode = [NSUserDefaults.standardUserDefaults integerForKey:@"appMode"];
+    LKAppMode appMode = [self getCurrentAppMode];
     [self setCurrentAppMode:appMode];
 
     [AppReadiness runNowOrWhenAppDidBecomeReady:^{

Session/Meta/AppDelegate.swift

@@ -40,4 +40,20 @@ extension AppDelegate {
     @objc func stopClosedGroupPoller() {
         ClosedGroupPoller.shared.stop()
     }
+    
+    @objc func getAppModeOrSystemDefault() -> AppMode {
+        let userDefaults = UserDefaults.standard
+        
+        guard userDefaults.dictionaryRepresentation().keys.contains("appMode") else {
+            if #available(iOS 13.0, *) {
+                return UITraitCollection.current.userInterfaceStyle == .dark ? .dark : .light
+            } else {
+                return .light
+            }
+        }
+        
+        let mode = userDefaults.integer(forKey: "appMode")
+        return AppMode(rawValue: mode) ?? .light
+    }
+    
 }