Add NGO networking with owner-authoritative player position sync

Install Netcode for GameObjects 2.13.0 + Unity Transport 2.6.0 and wire up
the first networking milestone: syncing player position/rotation across clients.

- NetworkBootstrap: Host/Client/Server controls (OnGUI + H/C hotkeys) for
  local clone testing over loopback 127.0.0.1:7777.
- NetworkPlayerSetup: per-avatar owner gating. The local owner binds the
  GameModeManager and cameras to itself; remote avatars disable their
  controller/CharacterController and receive transform via NetworkTransform.
- GameModeManager.BindLocalPlayer: central runtime rebind to the locally
  spawned player.
- FirstPersonController.SetPlayer: explicit runtime rebind hook.
- Player prefab: NetworkObject + NetworkTransform (owner-authoritative,
  position + rotation) + NetworkPlayerSetup; registered as PlayerPrefab.
- Scene: NetworkManager + UnityTransport added; the fixed scene player
  instance removed in favor of spawn-on-connect.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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