Add first-person camera mode with pose-aware eye offset and yaw facing

Introduce a FirstPersonController / FirstPersonMode pair (mirroring the
free-cam mode) wired into the GameModeManager Tab cycle. In first person the
mesh is hidden, the eye sits on CameraTarget plus a per-pose
firstPersonCameraTargetYOffset, and the character body yaw is driven to match
the camera via a new single-writer FaceYaw hook on PlayerCharacterController.

Also includes user content edits (poses, prefabs, scene) carried along.

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

Assets/Scripts/FirstPersonController.cs.meta

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