feat: add Phase 20a stage identities and overlap selection

scripts/characters/stickman/missing_stickman_placeholder.gd

@@ -3,12 +3,16 @@ extends Node2D
 
 var original_entry: Dictionary = {}
 var missing_stk_path: String = ""
+var stage_object_id: String = ""
+var stage_name: String = ""
 
 const MARKER_SIZE := Vector2(260.0, 52.0)
 
 func configure(entry: Dictionary) -> void:
 	original_entry = entry.duplicate(true)
 	missing_stk_path = String(entry.get("stk_path", ""))
+	stage_object_id = String(entry.get("stage_object_id", ""))
+	stage_name = String(entry.get("stage_name", ""))
 	queue_redraw()
 
 func get_area_rect() -> Rect2:

scripts/characters/stickman/stickman_rig.gd

@@ -226,6 +226,10 @@ var action_queue: Array[Dictionary]:
 
 ## Original .stk asset path, assigned by StageSpawner for scene persistence.
 var source_stk_path: String = ""
+## Persistent per-stage-instance identity and display name. Reusable .stk
+## assets never serialize these fields.
+var stage_object_id: String = ""
+var stage_name: String = ""
 
 ## Authored nonvisual subsystem children. They establish explicit ownership
 ## boundaries while this facade preserves the long-standing public API.