Garmr/radiance daemon refactor

[garmr-ulfr]

Summary

• Migrate lantern to radiance's new IPC Client architecture: All client-related functionality now goes through
  radiance/ipc.Client instead of directly calling radiance internals (radiance.Radiance, vpn.* package-level functions,
  api.APIClient, etc.)
• Rewrite lantern-core/core.go: LanternCore now wraps *ipc.Client with platform-specific initialization via build
  tags (init_mobile.go for iOS/Android/macOS, init_desktop.go for Linux). All VPN, account, server, split tunnel, and
  settings operations delegate to the IPC client.
• Update all call sites: vpn_tunnel, mobile, ffi (Linux and non-Linux), private-server, and wintunmgr packages
  updated to use ipc.Client methods instead of old radiance package-level calls.
• Update iOS/macOS network extensions: Start the IPC server (MobileStartIPCServer) before VPN operations in
  startTunnel, and close it (MobileCloseIPCServer) in stopTunnel.