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  superseded BEAR_*.tres, marketing/spare PNGs, a spare font weight and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

art/levels/arena_wall.png.import

@@ -0,0 +1,45 @@
+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://dm1okamastgng"
+path.s3tc="res://.godot/imported/arena_wall.png-f64c5b0c4dea0a0dcf6990f8e3c784c1.s3tc.ctex"
+path.etc2="res://.godot/imported/arena_wall.png-f64c5b0c4dea0a0dcf6990f8e3c784c1.etc2.ctex"
+metadata={
+"imported_formats": ["s3tc_bptc", "etc2_astc"],
+"vram_texture": true
+}
+generator_parameters={
+"md5": "0e7ed34c3c812d96732bd32f9dca0c93"
+}
+
+[deps]
+
+source_file="res://art/levels/arena_wall.png"
+dest_files=["res://.godot/imported/arena_wall.png-f64c5b0c4dea0a0dcf6990f8e3c784c1.s3tc.ctex", "res://.godot/imported/arena_wall.png-f64c5b0c4dea0a0dcf6990f8e3c784c1.etc2.ctex"]
+
+[params]
+
+compress/mode=2
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/uastc_level=0
+compress/rdo_quality_loss=0.0
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=true
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/channel_remap/red=0
+process/channel_remap/green=1
+process/channel_remap/blue=2
+process/channel_remap/alpha=3
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=0