NS-23: Skip move_and_slide when idle on floor (stop rest jitter)

Zero-velocity move_and_slide each physics tick still reapplies floor snap and
collision, which often reads as vibration. If there is no walk goal (or we
just arrived), velocity is zero, and is_on_floor(), return early.

client/scripts/player.gd

@@ -7,6 +7,9 @@ extends CharacterBody3D
 ## distance, bounds) is server MoveCommand only — not reimplemented here.
 ##
 ## Nav detours except when goal Y is below us: then xz toward goal (waypoints sit under bump rims).
+##
+## Idle: skip `move_and_slide()` when on floor and velocity is zero — repeated slide + floor snap
+## causes visible micro-vibration at rest.
 
 const MOVE_SPEED: float = 5.0
 const ARRIVE_EPS: float = 0.35
@@ -54,9 +57,15 @@ func _set_horizontal_velocity_toward(point: Vector3) -> void:
 	velocity.y = 0.0
 
 
+func _skip_move_when_idle_on_floor() -> bool:
+	return is_on_floor() and velocity.length_squared() < 1e-12
+
+
 func _physics_process(_delta: float) -> void:
 	if not _has_walk_goal:
 		velocity = Vector3.ZERO
+		if _skip_move_when_idle_on_floor():
+			return
 		move_and_slide()
 		return
 
@@ -67,6 +76,8 @@ func _physics_process(_delta: float) -> void:
 		velocity = Vector3.ZERO
 		_has_walk_goal = false
 		_nav_agent.set_target_position(global_position)
+		if _skip_move_when_idle_on_floor():
+			return
 		move_and_slide()
 		return