Add Godot level editing save path

TASKS.md

@@ -146,6 +146,10 @@ This backlog tracks what must change so the implementation matches `docs/design.
 - [x] Add test/build helpers for level construction.
   - Prefer shared builders for linear networks, forks, leaks, wall electricity faces, doors, controls, consumers, and reactors.
   - Avoid duplicating low-level array setup across tests.
+- [x] Add Godot level editing support.
+  - Expose editor tool, carrier, and remedy selection from the level screen.
+  - Apply `LevelEditor` commands to grid clicks in edit mode.
+  - Validate and save edited levels back through `LevelSerializer`.
 
 ## P1 Godot UX Integration