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

ui/damage_vignette.gdshader

@@ -0,0 +1,16 @@
+shader_type canvas_item;
+
+// Faint red gradient hugging the screen edges, flashed on a hit. `flash` is tweened
+// 0.9 → 0 by the HUD; the vignette is transparent in the centre and reddens toward
+// the corners so the middle of the screen stays clear.
+uniform float flash : hint_range(0.0, 1.0) = 0.0;
+uniform vec3 tint : source_color = vec3(0.75, 0.0, 0.0);
+uniform float inner : hint_range(0.0, 1.0) = 0.45;
+uniform float outer : hint_range(0.0, 1.0) = 1.0;
+
+void fragment() {
+	// Distance from centre normalised so the corners land at ~1.0.
+	float dist = length(UV - vec2(0.5)) / 0.70710678;
+	float v = smoothstep(inner, outer, dist);
+	COLOR = vec4(tint, v * flash);
+}