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/stickman_editor.gd

@@ -53,7 +53,7 @@ const FILE_FILTER := "*.stk ; Stickman Files"
 
 const SUPPORTED_VERSIONS: Array[String] = ["1.0", "1.1", "1.2", "1.3", "1.4", "1.5"]
 
-# Phase 8: rig proportions (master_rig.tscn rest pose — see spec §2).
+# Phase 8: rig proportions (scenes/stickman_rig.tscn rest pose — see spec §2).
 const PROPORTIONS: Dictionary = {
 	"upper_arm_length": 168.0,
 	"lower_arm_length": 200.0,