Implement interactive prop handling for StickmanRig

- Added PropTrajectory class for deterministic ballistic calculations.
- Introduced StickmanPropInteraction component to manage prop interactions (pickup, drop, throw).
- Implemented grip resolution and attachment logic for props.
- Added signals for interaction events (prop_picked_up, prop_dropped, prop_thrown).
- Defined specifications for prop interaction lifecycle and event rules.
- Ensured compatibility with existing prop systems and added new capabilities for prop pickup.

scripts/stage_spawner.gd

@@ -176,6 +176,8 @@ func spawn_prop_asset(asset_id: String, object_position: Vector2) -> PropBlock:
 	else:
 		prop = PROP_UTILS.spawn_prop(_world, object_position, template["payload"], int(template["material_preset"]), Vector2.ZERO)
 	prop.spawn_id = String(template.get("id", asset_id))
+	prop.anchors = template.get("anchors", {}).duplicate(true)
+	prop.can_be_picked_up = bool(template.get("can_be_picked_up", true))
 	return prop