Move Blender sources under art/blender and snake_case them

Relocate the Blender working files into art/blender/ (Godot-ignored via
the .gdignore that travels with them) and lowercase the ANIM_* files to
snake_case: anim_bull, anim_bull2, anim_matador, anim_publik_mees. Drop
the stray matador2.gd.uid (no matador2.gd exists).

Repoint .gitignore (preview + blend-backup patterns), render_anim_preview.py
and CLAUDE.md at art/blender/, and update the anim-doc references from the
deleted matador_v02 to matador_v03.

No game impact: art/blender/ sits outside Godot's import graph (confirmed:
no .blend imported, preview stays gitignored, menu boots clean).

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

.gitignore

@@ -9,10 +9,10 @@
 .idea/
 
 # Blender render previews (generated by render_anim_preview.py)
-Blender/preview/
+art/blender/preview/
 
 # Blender auto-save backups (.blend1, .blend2, … — Blender rewrites these on every save)
-Blender/*.blend[0-9]
+art/blender/*.blend[0-9]
 
 # Test output (generated screenshots, frame strips)
 tests/output/