Reorganize into role-based folders and consolidate art

Move every script and scene into role-based directories (actors/, systems/, ui/,
levels/, props/) and all raw art under art/ (grouped by role, snake_case,
Extract-Textures GLBs), dropping Blender version-suffix noise. Filenames are
snake_case (PascalCase reserved for class_name) to avoid case-insensitive
filesystem aliasing on the web/macOS targets. Routes the bull's hits through the
typed DamageEvent pipeline and wires the bull's abilities to the Fx library.
Updates CLAUDE.md's folder-layout overview to match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CCyaJPTHCH9EDthpf4A5Sj

levels/level_def.gd

@@ -1,9 +1,8 @@
 class_name LevelDef
 extends Resource
-## Definition of one playable level on the run map — the arena today, later a cave with
-## a bear, a china shop to smash, and so on. Every map node references a LevelDef, and
-## the map/flow code never hard-codes a scene: adding a level is a new LevelDef (plus its
-## scene) handed out by the map generator in run_state.gd.
+## Definition of one playable level — the arena, the bear's den, the lobby hub, and later
+## a china shop to smash. The flow code never hard-codes a scene: a level is a LevelDef
+## (plus its scene) built in run_state.gd and served through the lobby.
 
 @export var id: StringName = &""
 @export var display_name: String = "Level"
@@ -15,14 +14,10 @@ extends Resource
 ## colliders and any level-specific subscripts. Swapped wholesale between levels so no
 ## previous level's geometry (or its colliders) can leak into the next.
 @export var level_scene: PackedScene = null
-## Placeholder pip tint on the map until per-level icon art exists.
-@export var color: Color = Color(0.80, 0.62, 0.24)
 ## Camera framing multiplier when this level loads — 1.0 is the shell camera's default
 ## shot; >1 dollies the camera back for a wider view (the lobby pulls out so the whole
 ## hub reads). Applied by game_shell; independent of the player's scroll-wheel zoom.
 @export var camera_zoom: float = 1.0
-## A boss level caps a run — its node is drawn larger and clearing it ends the map.
-@export var is_boss: bool = false
 ## The enemy this level pits the bull against. Null → the usual matador wave (the
 ## spawner's default). Set → a single boss enemy of this scene is spawned instead (e.g.
 ## the bear), and the fight is won when it falls. The arena scene is shared either way;