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  superseded BEAR_*.tres, marketing/spare PNGs, a spare font weight and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

systems/input/touch_controls.gd

@@ -28,10 +28,10 @@ const _MOVE_FORWARD: StringName = &"move_forward"
 
 # Ability slots in player.gd order: kick=0, dash=1, slam=2, roll=3.
 const _ABILITY_ICONS: Array[String] = [
-	"res://HUD/KICK.png",
-	"res://HUD/DASH.png",
-	"res://HUD/SLAM.png",
-	"res://HUD/ROLL.png",
+	"res://art/icons/kick.png",
+	"res://art/icons/dash.png",
+	"res://art/icons/slam.png",
+	"res://art/icons/roll.png",
 ]
 const _ABILITY_LETTERS: Array[String] = ["K", "D", "S", "R"]
 const _ABILITY_ACCENT: Array[Color] = [