Move bull ability FX into the authorable systems/fx/ library

The bull's kick/dash/slam/roll and movement particles were ~112 lines of
hand-built CPUParticles3D in player.gd, bypassing the Fx system entirely
(Fx.spawn had zero callers) — so Siim couldn't author them in the inspector.

- Add six inspector-editable effect scenes (bull_slam/kick/dash one-shots +
  bull_hoof_dust/charge_trail/roll_sparks continuous); wire player.gd to
  Fx.spawn() / new Fx.attach(); register them + the gallery + smoke test.
- Extract the coded, non-particle slam rings + kick flash into a new
  bull_impact_fx.gd component (bull_legs.gd pattern).
- Drop 12 now-obsolete DP dust look-params (the .tscn owns the look now).
- Trim god-file comment noise: rewrite an AI-placeholder barrel block to typed
  code, drop dead commented-out bounce/topple code, fix stale post-reorg file
  paths (Assets/… → art/…, PascalCase scene names → snake_case).
- Document the Siim workflow in systems/fx/README.md; update CLAUDE.md.

player.gd 1307 → 944 lines. Full suite green.

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

systems/fx/effect_gallery.gd

@@ -4,7 +4,10 @@ extends Node3D
 ## 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"]
+const _EFFECTS: Array[StringName] = [
+	&"blood_burst", &"slam_dust", &"spark", &"hit_flash",
+	&"bull_slam", &"bull_kick", &"bull_dash",
+]
 
 @onready var _label: Label = $UI/Label
 # Reached by path rather than the Fx global so the placeholder-seeder can compile and attach this