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/GameModeManager.cs

@@ -25,6 +25,9 @@ public class GameModeManager : MonoBehaviour
     [Tooltip("Free-fly spectator camera. Empty = found automatically. Absent = Free Cam is left out of the cycle.")]
     public FreeCamController freeCam;
 
+    [Tooltip("First-person camera. Empty = found automatically. Absent = First Person is left out of the cycle.")]
+    public FirstPersonController firstPerson;
+
     //[Tooltip("Insect / surface-walk controller. Empty = found automatically.")]
     //public InsectController insect;
 
@@ -43,6 +46,7 @@ public class GameModeManager : MonoBehaviour
     public ThirdPersonOrbitInput CameraInput => cameraInput;
     public MeshPainter Painter => painter;
     public FreeCamController FreeCam => freeCam;
+    public FirstPersonController FirstPerson => firstPerson;
     //public InsectController Insect => insect;
 
     /// <summary>Raised after a mode switch finishes (the new mode's Enter has already run).
@@ -63,6 +67,7 @@ public class GameModeManager : MonoBehaviour
         if (!painter) painter = FindFirstObjectByType<MeshPainter>();
         // Include inactive so a freecam rig that starts disabled is still found and wired.
         if (!freeCam) freeCam = FindFirstObjectByType<FreeCamController>(FindObjectsInactive.Include);
+        if (!firstPerson) firstPerson = FindFirstObjectByType<FirstPersonController>(FindObjectsInactive.Include);
         //if (!insect) insect = FindFirstObjectByType<InsectController>();
 
         BuildModes();
@@ -90,6 +95,10 @@ public class GameModeManager : MonoBehaviour
         if (freeCam)
             _modes.Add(new FreeCamMode());
 
+        // First Person only joins the cycle when a first-person rig is present, so scenes without one are unchanged.
+        if (firstPerson)
+            _modes.Add(new FirstPersonMode());
+
         // Insect mode only joins the Tab cycle when a surface walker is present, so a scene
         // without one behaves exactly as before (no dead, player-freezing mode in the cycle).
         //if (insect)