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/fx/effect_gallery.gd

@@ -0,0 +1,30 @@
+extends Node3D
+## Live preview stage for the FX library. Cycles through every registered effect on a loop against
+## arena-ish lighting so Siim sees each one as it reads in-game. Open fx/effect_gallery.tscn and
+## press Play, then edit any effect .tscn in the inspector and re-run to compare. See fx/README.md.
+
+const _CYCLE_SEC := 1.6
+const _EFFECTS: Array[StringName] = [&"blood_burst", &"slam_dust", &"spark", &"hit_flash"]
+
+@onready var _label: Label = $UI/Label
+# Reached by path rather than the Fx global so the placeholder-seeder can compile and attach this
+# script headless (autoload globals aren't resolvable during an on-demand compile in a --script run).
+@onready var _fx: Node = get_node("/root/Fx")
+
+var _index := 0
+
+
+func _ready() -> void:
+	var timer := Timer.new()
+	timer.wait_time = _CYCLE_SEC
+	timer.autostart = true
+	add_child(timer)
+	timer.timeout.connect(_fire_next)
+	_fire_next()
+
+
+func _fire_next() -> void:
+	var effect := _EFFECTS[_index % _EFFECTS.size()]
+	_index += 1
+	_label.text = "%s   (%d/%d)" % [effect, (_index - 1) % _EFFECTS.size() + 1, _EFFECTS.size()]
+	_fx.call("spawn", effect, global_transform.translated_local(Vector3(0.0, 0.25, 0.0)))