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.

.gitignore

@@ -0,0 +1,6 @@
+.DS_Store
+DerivedData/
+xcuserdata/
+*.xcresult
+build/
+.swiftpm/