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/bull_slam.tscn

@@ -0,0 +1,47 @@
+[gd_scene format=3]
+
+; Bull ground-slam dust — the one-shot dirt burst thrown up when the slam lands. Fired via
+; Fx.spawn(&"bull_slam", xform) at the impact point. The expanding shockwave RINGS are a
+; separate coded effect (actors/player/bull_impact_fx.gd), not this. Tune the look here.
+
+[ext_resource type="Script" path="res://systems/fx/one_shot_effect.gd" id="oneshot"]
+
+[sub_resource type="StandardMaterial3D" id="mat"]
+transparency = 1
+cull_mode = 2
+shading_mode = 0
+vertex_color_use_as_albedo = true
+
+[sub_resource type="SphereMesh" id="mesh"]
+material = SubResource("mat")
+radius = 0.09
+height = 0.18
+radial_segments = 4
+rings = 2
+
+[sub_resource type="Curve" id="curve"]
+_data = [Vector2(0, 0.25), 0.0, 0.0, 0, 0, Vector2(0.35, 1.6), 0.0, 0.0, 0, 0, Vector2(1, 0), 0.0, 0.0, 0, 0]
+point_count = 3
+
+[sub_resource type="Gradient" id="grad"]
+colors = PackedColorArray(0.88, 0.74, 0.46, 1, 0.88, 0.74, 0.46, 0)
+
+[node name="bull_slam" type="CPUParticles3D"]
+emitting = false
+amount = 48
+lifetime = 1.1
+one_shot = true
+local_coords = false
+explosiveness = 0.85
+randomness = 0.5
+mesh = SubResource("mesh")
+direction = Vector3(0, 1, 0)
+spread = 85.0
+gravity = Vector3(0, -7, 0)
+initial_velocity_min = 3.5
+initial_velocity_max = 10.0
+scale_amount_min = 0.5
+scale_amount_max = 2.0
+scale_amount_curve = SubResource("curve")
+color_ramp = SubResource("grad")
+script = ExtResource("oneshot")