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

CLAUDE.md

@@ -43,7 +43,9 @@ art/                            all raw art, grouped by role (snake_case):
 | `levels/arena_level.tscn` | The arena **level module**: floor + wall colliders, arena meshes, `MatadorSpawner` (with child `Node3D` spawn points placed by the designer), lighting, audience (`PublikNode`). Instanced into the shell's `LevelRoot` |
 | `levels/bear_level.tscn` | The Bear's Den **level module**: bear-arena mesh, its own floor collider, lighting, and a `BearSpawner` (`bear_spawn.gd`) that places the bear at center. Instanced into the shell's `LevelRoot` |
 | `actors/player/player.tscn` | Player scene root (`CharacterBody3D`) |
-| `actors/player/player.gd` | Movement, charge, turning logic |
+| `actors/player/player.gd` | Movement, charge, turning, and abilities (kick/dash/slam/roll). Ability & movement particle FX are **not** built here — they're authored scenes in `systems/fx/` (`bull_*.tscn`), fired via `Fx.spawn()` (one-shots) / `Fx.attach()` (continuous) |
+| `actors/player/bull_impact_fx.gd` | Bull's coded, non-particle impact FX (the slam shockwave rings + kick flash-pop — tweened meshes, not CPUParticles3D, so they can't be `systems/fx/` scenes). Created by `player.gd` |
+| `actors/player/bull_legs.gd` | Bull body-wobble + tail Verlet-chain simulation. Created by `player.gd` |
 | `camera_spring_arm.gd` | Mouse-look pivot (`Node3D` + `SpringArm3D`) |
 | `camera_follow.gd` | Smooth camera follow (`Camera3D`) |
 | `actors/matador/matador.gd` | Matador AI (wander / ragdoll state machine) |