Implement Phase 8: Rig Relocation and Component Modularization

- Moved the rig scene from `res://master_rig.tscn` to `res://scenes/stickman_rig.tscn`, preserving its UID.
- Split the `StickmanRig` controller into three components: `StickmanLocomotion`, `StickmanRagdoll`, and `StickmanActionRunner`.
- Updated the architecture to ensure `StickmanRig` acts as the public facade for the new components.
- Created a new test suite `test_phase8_rig_modularization.gd` to verify the integrity of the relocated rig and its components.
- Added checks for scene loading, component resolution, action queue delegation, and state authority.

scripts/physics_test_harness.gd

@@ -3,7 +3,7 @@ extends Node2D
 ## PhysicsTestHarness - Standalone vector-terrain physics test scene (Phase 2).
 ##
 ## Builds flat ground, an angled ramp and stepped terrain via the TerrainUtils
-## factory, spawns a master_rig.tscn instance standing on the flat ground, and
+## factory, spawns a scenes/stickman_rig.tscn instance standing on the flat ground, and
 ## provides camera zoom/pan input plus a top-bar UI (spawn buttons, a
 ## Stickman/Ragdoll mode toggle, and a "Knock Up" force button). NOT wired into
 ## the editor — run standalone via F6 on res://scenes/physics_test_harness.tscn.
@@ -16,7 +16,7 @@ const MIN_ZOOM: float = 0.25
 const MAX_ZOOM: float = 3.0
 const ZOOM_STEP: float = 1.10
 
-const RIG_SCENE := preload("res://master_rig.tscn")
+const RIG_SCENE := preload("res://scenes/stickman_rig.tscn")
 
 ## Preloaded prop scripts: resolved via preload (not the global class registry)
 ## so the harness compiles even when the editor's class cache is stale.
@@ -251,7 +251,7 @@ func _build_environment() -> void:
 func _spawn_rig() -> void:
 	var rig := RIG_SCENE.instantiate() as StickmanRig
 	if rig == null:
-		push_warning("PhysicsTestHarness: failed to instantiate master_rig.tscn.")
+		push_warning("PhysicsTestHarness: failed to instantiate scenes/stickman_rig.tscn.")
 		return
 	rig.position = RIG_SPAWN_POSITION
 	# Manual recovery only ("Recover Now"): auto-recover is left off so the