Reorganize the codebase into role-based folders (snake_case)

Move the 40-odd root-level scripts and scenes into a tree that groups by role,
per the approved roadmap (WS2/WS3): actors/{player,matador,bear}, systems/{combat,
fx,input,debug,render,crowd,config}, ui/, props/ (was tscn_s/). Rename the shell
scene.tscn -> levels/game_shell.tscn and every PascalCase scene to snake_case
(Player.tscn -> player.tscn, MainMenu.tscn -> main_menu.tscn, etc.) so the
case-insensitive web/macOS filesystems can't alias two files together.

Done as a scripted move: each file travels with its .uid; every quoted res:// path
across scenes, scripts, .tres, and project.godot's 9 autoloads is rewritten; the
.godot uid/class cache is rebuilt from scratch. Scenes still resolve by uid, so the
rewrite is belt-and-suspenders. Lint globs (run_tests.sh + both CI workflows) now
walk the new dirs; an orphan animation_tree.gd.uid and 7 pre-existing trailing-
whitespace lints (barrel/torch, never covered by the old root-only glob) are cleaned.

Full suite green on both sides. Asset consolidation (Assets/Animations/fonts ->
art/) is deferred — moving imported .glb/.png/.ttf is safer done in the editor.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017KoYBYQgRyY1zDHXMsXY3V

systems/combat/physics_layers.gd

@@ -0,0 +1,11 @@
+## Central registry of the 3D physics collision-layer bits. These mirror the
+## layer_names in project.godot so the editor's layer picker reads the same words.
+##
+## The bull only collides with WORLD, so a killed matador is lifted off WORLD onto
+## CORPSE alone (see matador_ragdoll.gd). The ground and walls carry WORLD | CORPSE
+## (tagged at level load in game_shell.gd), so the ragdoll still rests on the arena
+## while the bull passes through the bodies instead of tripping over them.
+
+const WORLD:  int = 1  # layer 1 — environment + live actors (bull, matadors, spears)
+const BULL:   int = 2  # layer 2 — the bull's own body
+const CORPSE: int = 4  # layer 3 — ragdolled matadors; ground/walls also carry this