chore: scaffold Voice iOS app (Phase 0)

XcodeGen project, SwiftUI iOS 17 target dev.shane.voice, SPM
livekit-client-swift 2.16.0, mic usage + ATS LAN exception in
Info.plist, placeholder conversation screen and Settings with
server URL field.

Sources/App/VoiceApp.swift

@@ -0,0 +1,13 @@
+import SwiftUI
+
+@main
+struct VoiceApp: App {
+    @StateObject private var settings = SettingsStore()
+
+    var body: some Scene {
+        WindowGroup {
+            ConversationView(settings: settings)
+                .preferredColorScheme(.dark)
+        }
+    }
+}