Third-person camera + fix the avatar customize preview

You couldn't see your own character because the camera was first-person
(inside the avatar's head), and the customize screen's 3D preview rendered
nothing.

- player.tscn: camera now hangs off a SpringArm3D on a CameraPivot, 4 m
  behind + above the player, pulled in on collision. player.gd: yaw still
  turns the body, pitch orbits the arm (starts tilted down to frame the
  avatar).
- avatar_customization_ui.gd: the preview SubViewport had own_world_3d=false,
  so it shared the Control-only main world -- no scenario, nothing rendered.
  Set own_world_3d=true, add a WorldEnvironment with ambient fill + a
  key/fill light pair, make the camera current, tweak framing.
- smoke_test_player: assert the third-person SpringArm rig (18/18).
- smoke_test_enter_world: wait longer for the scene change -- a real
  POST /join spawns a dedicated server, which is slow (9/9).

Client-side change -- rebuild the exe to get it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015jtxAiu5dAW4WxCNdGkrkJ

scripts/smoke_test_enter_world.gd

@@ -81,7 +81,7 @@ func _run() -> void:
 		return
 
 	enter_button.pressed.emit()
-	await _wait_for_scene_change(instance, 60)
+	await _wait_for_scene_change(instance, 600)  # generous -- a real POST /join may spawn a dedicated server (slow)
 
 	var game_scene := current_scene
 	if not _check("game.tscn became current_scene after Enter World", game_scene != null and game_scene != instance):