Consolidate raw art under art/ and prune unused assets

Group all raw art by role under art/ (characters, levels, weapons, fx,
anim, textures, ui, icons, fonts, hdri, materials), matching the earlier
code reorg. Files are snake_case; asset uids are preserved so uid:// refs
still resolve, and every res:// path reference is rewritten across scenes,
scripts and project.godot.

- Move the used assets out of Assets/ Animations/ fonts/ HUD/ HDRI/
  Materials/ into art/; remove those dirs.
- Materials snake_cased: barrel_metal, barrel_wood, bear_claw_fx, fire.
- Delete unreferenced assets: alternate models, empty stub scripts,
  superseded BEAR_*.tres, marketing/spare PNGs, a spare font weight and
  the orphan M_Barrel_wood.gdshader.
- Blender: drop .blend auto-backups and matador_v01/v02 (+ stale v02 fbx);
  keep matador_v03 and repoint create_matador_anims.py to it. .gitignore
  now blocks all Blender/*.blend[0-9] backups.
- GLB Extract-Textures siblings (art/levels/*.png) kept and tracked.
- Document the art/ layout in CLAUDE.md.

Headless suite green; menu and gameplay shell boot clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FBbGXbzg3SD6ZBSadPPF5H

levels/bear_level.tscn

@@ -1,6 +1,6 @@
 [gd_scene format=3 uid="uid://dfxigg3cr6nl5"]
 
-[ext_resource type="PackedScene" uid="uid://bm6rmt3xprhjs" path="res://Assets/bear_level_arena.glb" id="1_beararena"]
+[ext_resource type="PackedScene" uid="uid://bm6rmt3xprhjs" path="res://art/levels/bear_arena.glb" id="1_beararena"]
 [ext_resource type="Script" uid="uid://bbtlwihtlc1wp" path="res://levels/bear_spawn.gd" id="2_spawn"]
 [ext_resource type="PackedScene" uid="uid://o8ocjfprxa7u" path="res://actors/bear/bear.tscn" id="3_bear"]
 [ext_resource type="Script" uid="uid://dfk7dcvki7rqu" path="res://levels/bear_hud.gd" id="4_bearhud"]