Remove editor autosave cruft and orphan scenes

Delete 17 tracked *.tmp editor autosaves and three verified-unreferenced
orphans (Assets/bear_level.tscn, Assets/matador_2.tscn, matador_2.gd), and
gitignore *.tmp so they never return. The real Assets/bear_level_arena.glb is
kept — it still backs levels/bear_level.tscn.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CmG3mQGVXZUPDVapmdbWZ1

.gitignore

@@ -2,6 +2,9 @@
 .godot/
 /android/
 
+# Godot editor autosave scratch files (e.g. Bear.tscn12015901897.tmp)
+*.tmp
+
 # JetBrains IDE — contains absolute paths (Godot binary, SDK dirs), varies per user
 .idea/