fix(ios): add AppIcon asset catalog and fix launch screen for TestFlight

Adds Assets.xcassets with a placeholder 1024x1024 AppIcon so Xcode
compiles CFBundleIconName and the required icon sizes into the bundle.
Replaces UILaunchStoryboardName (missing storyboard) with UILaunchScreen
dict, valid for iOS 14+ (min target is iOS 18). Fixes all four App Store
Connect validation errors blocking TestFlight upload.

clients/apple/iOS/VoiceCatiOS/Assets.xcassets/Contents.json

@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}