Add per-pose fall animation state and clip

Play a dedicated falling animation when the player is airborne and
descending past a scale-aware velocity threshold.

- PlayerCharacterController: new IsFalling state + Fall Animation Speed
  threshold (true only when !grounded && !wallClimbing && descending,
  scaled via CapsuleScale); explicitly false during wall/ceiling climb.
- PlayerPose: per-pose Fall Clip + Fall Clip Speed (mirrors walk/run).
- PlayerPoseController: select the fall clip while falling, fall back to
  the idle clip when a pose has none (no regression).
- Author content: Paintman-Fall.anim assigned to Pose_Idle; UMotion
  project, Player prefab and scene authoring.
- Docs: check off the fall animation in GAME_DESIGN.md.

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

Assets/Scripts/PlayerCharacterController.cs

@@ -71,6 +71,10 @@ public partial class PlayerCharacterController : MonoBehaviour
     [Tooltip("Small downward velocity kept while grounded for reliable ground contact.")]
     public float groundedStickVelocity = -2f;
 
+    [Tooltip("Downward speed (units/second) past which the player counts as falling, for the fall " +
+             "animation. Only while airborne (not grounded, not wall-climbing). Scales with player size.")]
+    public float fallAnimationSpeed = 4f;
+
     [Header("Slope Sliding")]
     [Tooltip("Slide down surfaces steeper than the CharacterController's Slope Limit instead of balancing on them.")]
     public bool slideDownSteepSlopes = true;
@@ -177,6 +181,13 @@ public partial class PlayerCharacterController : MonoBehaviour
     /// </summary>
     public bool IsMovingOnGround => _movingOnGround;
 
+    /// <summary>
+    /// True while airborne and descending faster than <see cref="fallAnimationSpeed"/> (scaled by player
+    /// size): not grounded and not wall-climbing. Rising after a jump, standing, moving on the ground, and
+    /// wall/ceiling states all read false. Exposed so the pose system can pick its fall clip.
+    /// </summary>
+    public bool IsFalling => _isFalling;
+
     /// <summary>
     /// Set by <see cref="PlayerPoseController"/> while a pose Playable graph owns the Animator output.
     /// While set, the run-bool is not poked: it would be moot (the graph overrides it) and Unity would
@@ -211,6 +222,7 @@ public partial class PlayerCharacterController : MonoBehaviour
     private bool _sprinting;              // sprint key state this frame (exposed via IsSprinting)
     private bool _isIdle;                 // snapshot: player essentially still this frame (exposed via IsIdle)
     private bool _movingOnGround;         // snapshot: grounded & moving above the run threshold (exposed via IsMovingOnGround)
+    private bool _isFalling;              // snapshot: airborne & descending past the fall threshold (exposed via IsFalling)
     private float _groundOffset;          // signed vertical mesh raise from the ground mouse pose-adjust (+ up / - down); folded into SetMeshLean
 
     // Ground contact normal from the latest Move (for slope sliding).
@@ -367,6 +379,7 @@ public partial class PlayerCharacterController : MonoBehaviour
             _horizontalVelocity = Vector3.zero; // drop ground momentum so resuming starts from rest
             _isIdle = ControlEnabled && (h * h + v * v) <= 1e-4f; // attached & no climb input = holding a pose
             _movingOnGround = false;            // on a wall/ceiling, never ground locomotion
+            _isFalling = false;                 // attached to a surface, not falling
             return;
         }
 
@@ -453,6 +466,9 @@ public partial class PlayerCharacterController : MonoBehaviour
         bool movingOnGround = _controller.isGrounded && horizontalVel.sqrMagnitude > RunningSpeedThresholdSqr;
         _movingOnGround = movingOnGround;
         _isIdle = ControlEnabled && _controller.isGrounded && !movingOnGround; // standing still on the floor
+        // Falling: airborne and descending past the threshold (wall-climb already returned above, so
+        // not-grounded here means free in the air). Scaled by player size like gravity/jump.
+        _isFalling = !_controller.isGrounded && _verticalVelocity < -fallAnimationSpeed * CapsuleScale;
     }
 
     /// <summary>