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.

opencode.json

@@ -0,0 +1,11 @@
+{
+  "$schema": "https://opencode.ai/config.json",
+  "mcp": {
+    "xcodebuildmcp": {
+      "type": "local",
+      "command": ["/Users/shane/.local/bin/xcodebuildmcp", "mcp"],
+      "enabled": true,
+      "environment": {}
+    }
+  }
+}