Save The Tree implementation and acceptance work in progress

Preserve production code, regression fixtures, audio assets and provenance, test infrastructure, and the original-completion plan and progress ledger. Final game and Windows acceptance remain pending; excluded local artifacts and native experiments are not part of this snapshot.

scripts/core/state_transaction.gd

@@ -62,7 +62,7 @@ func stage_dictionary_set(
 			return true,
 		func() -> void:
 			if had_key:
-				target[key] = original_value
+				target[key] = _copy_value(original_snapshot)
 			else:
 				target.erase(key)
 	)
@@ -94,7 +94,7 @@ func stage_dictionary_erase(
 			return true,
 		func() -> void:
 			if had_key:
-				target[key] = original_value
+				target[key] = _copy_value(original_snapshot)
 	)