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/spark.tscn

@@ -0,0 +1,40 @@
+[gd_scene format=3]
+
+[ext_resource type="Script" path="res://systems/fx/one_shot_effect.gd" id="1_kk3a7"]
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_tjifq"]
+transparency = 1
+cull_mode = 2
+shading_mode = 0
+vertex_color_use_as_albedo = true
+
+[sub_resource type="SphereMesh" id="SphereMesh_pv2r6"]
+material = SubResource("StandardMaterial3D_tjifq")
+radius = 0.03
+height = 0.06
+radial_segments = 4
+rings = 2
+
+[sub_resource type="Curve" id="Curve_l33bb"]
+_data = [Vector2(0, 1), 0.0, 0.0, 0, 0, Vector2(1, 0), 0.0, 0.0, 0, 0]
+point_count = 2
+
+[sub_resource type="Gradient" id="Gradient_pnkyn"]
+colors = PackedColorArray(1, 0.95, 0.6, 1, 1, 0.55, 0.1, 0)
+
+[node name="spark" type="CPUParticles3D" unique_id=69954641]
+emitting = false
+amount = 14
+lifetime = 0.35
+one_shot = true
+explosiveness = 1.0
+randomness = 0.6
+mesh = SubResource("SphereMesh_pv2r6")
+direction = Vector3(0, 1, 0)
+gravity = Vector3(0, -9, 0)
+initial_velocity_min = 3.0
+initial_velocity_max = 7.0
+scale_amount_min = 0.4
+scale_amount_curve = SubResource("Curve_l33bb")
+color_ramp = SubResource("Gradient_pnkyn")
+script = ExtResource("1_kk3a7")