fix(core): enforce CharacterData compile order and remove ClassDB type lookup on export

character.gd referenced CharacterData.State as a compile-time constant dict,
causing export to fail when character.gd was compiled before character_data.gd
(alphabetical order). The preload forces character_data.gd to be compiled first.
Changing SubResource type to "Resource" removes the ClassDB lookup for the
custom class name during scene export, relying on the explicit script reference
instead.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/characters/character.gd

@@ -1,6 +1,8 @@
 ## Character — base class for all playable figures (bunny, cat, etc.).
 class_name Character extends Node2D
 
+const _CharacterData = preload("res://scripts/characters/character_data.gd")
+
 signal character_picked_up(character: Character)
 signal character_placed(character: Character, position: Vector2)
 signal state_changed(new_state: CharacterData.State)