Replace MultipeerConnectivity with a custom P2P implementation using Network.framework (NWListener/NWConnection) and CoreBluetooth for discovery.
- Add P2PConnectionManager, BLEDiscoveryManager, and NetworkFraming.
- Add ConnectedPeer and DiscoveredHost models.
- Update Info.plist with local network and bluetooth permissions.
- Refactor Views to use P2PConnectionManager.
- Add implementation plan and transition docs.
