Add prop interaction system and throw mechanics specification

- Introduced `stickman_prop_interactor.gd` to manage prop interactions.
- Created `phase_11_prop_interactions.md` detailing the design and implementation of prop pickup, drop, and throw mechanics.
- Defined interaction states, action lifecycles, and event triggers for prop handling.
- Specified constraints for throw actions, including target positioning and velocity calculations.
- Established acceptance criteria for prop interactions and lifecycle management.

scripts/prop_library.gd

@@ -75,7 +75,7 @@ static func make_custom_entry(path: String) -> Dictionary:
 	var name := String(parsed.get("prop_name", "")).strip_edges()
 	if name.is_empty(): name = normalized_path.get_file().get_basename()
 	var preset: int = int(parsed.get("material_preset", PROP_BLOCK.MaterialPreset.NONE))
-	return {"id": normalized_path, "path": normalized_path, "name": name, "material_preset": preset, "material_label": PROP_FILE.preset_to_string(preset).capitalize(), "is_custom": true, "payload": PROP_FILE.flatten_to_payload(shapes), "shapes": shapes, "collision_hull": hull}
+	return {"id": normalized_path, "path": normalized_path, "name": name, "material_preset": preset, "material_label": PROP_FILE.preset_to_string(preset).capitalize(), "is_custom": true, "payload": PROP_FILE.flatten_to_payload(shapes), "shapes": shapes, "collision_hull": hull, "anchors": parsed.get("anchors", {})}
 
 
 static func is_custom_path(path: String) -> bool: