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/FirstPersonMode.cs

@@ -0,0 +1,41 @@
+/// <summary>
+/// First-person mode. The player keeps walking (WASD, camera-relative) but the camera moves to the
+/// player's eye (the CameraTarget) with free mouse-look, and the player's mesh is hidden so the body
+/// isn't seen from the inside. The orbit camera input is disabled while here so it doesn't fight for
+/// the cursor; the <see cref="FirstPersonController"/> drives its own dedicated CinemachineCamera.
+/// </summary>
+public class FirstPersonMode : GameMode
+{
+    public override string DisplayName => "First Person";
+
+    public override void Enter()
+    {
+        // Player stays fully controllable; only the view changes.
+        if (Manager.Player)
+        {
+            Manager.Player.enabled = true;
+            Manager.Player.ControlEnabled = true;
+        }
+
+        if (Manager.Painter)
+            Manager.Painter.PaintingEnabled = false;
+
+        // The orbit rig would otherwise keep grabbing the cursor and reading the mouse every frame.
+        if (Manager.CameraInput)
+            Manager.CameraInput.enabled = false;
+
+        if (Manager.FirstPerson)
+            Manager.FirstPerson.SetActive(true);
+    }
+
+    public override void Exit()
+    {
+        // Modes are Enter-only, so first-person must undo its own camera takeover (and unhide the mesh)
+        // here; the next mode's Enter restores the player/painter/look-mode state.
+        if (Manager.FirstPerson)
+            Manager.FirstPerson.SetActive(false);
+
+        if (Manager.CameraInput)
+            Manager.CameraInput.enabled = true;
+    }
+}