Reorganize into role-based folders and consolidate art

Move every script and scene into role-based directories (actors/, systems/, ui/,
levels/, props/) and all raw art under art/ (grouped by role, snake_case,
Extract-Textures GLBs), dropping Blender version-suffix noise. Filenames are
snake_case (PascalCase reserved for class_name) to avoid case-insensitive
filesystem aliasing on the web/macOS targets. Routes the bull's hits through the
typed DamageEvent pipeline and wires the bull's abilities to the Fx library.
Updates CLAUDE.md's folder-layout overview to match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CCyaJPTHCH9EDthpf4A5Sj

systems/crowd/crowd_billboard.gdshader

@@ -0,0 +1,35 @@
+shader_type spatial;
+// Flat crowd sprite. Each instance is oriented at build time to face the arena centre
+// (see crowd_billboards.gd) — NOT the camera — so spectators on different segments of
+// the ring face inward toward the action, like a real stand. Unshaded (the sheet was
+// baked with lighting), alpha-tested (no transparency sorting across hundreds of
+// quads), nearest-filtered for a crisp PS1 look that matches the ps1_filter effect.
+render_mode unshaded, cull_disabled, shadows_disabled, depth_draw_opaque;
+
+uniform sampler2D sheet : source_color, filter_nearest;
+uniform int hframes = 8;
+uniform float fps = 10.0;
+uniform float alpha_clip = 0.4;
+
+varying flat float v_frame;
+varying flat vec3 v_tint;
+
+void vertex() {
+	// Per-instance clap phase (0..1) and tint are packed into the MultiMesh custom data.
+	// The instance transform already carries the inward facing, so no billboard maths.
+	float phase = INSTANCE_CUSTOM.x;
+	v_tint  = INSTANCE_CUSTOM.yzw;
+	v_frame = floor(mod(TIME * fps + phase * float(hframes), float(hframes)));
+}
+
+void fragment() {
+	// Sheet is two rows: top = front, bottom = back. Show the back when the camera is
+	// behind the spectator (they're facing into the arena, away from us).
+	float u = (UV.x + v_frame) / float(hframes);
+	float v = UV.y * 0.5 + (FRONT_FACING ? 0.0 : 0.5);
+	vec4 c = texture(sheet, vec2(u, v));
+	if (c.a < alpha_clip) {
+		discard;
+	}
+	ALBEDO = c.rgb * v_tint;
+}