Remove the persistent blood-decal system

Strip only the floor/wall blood-splat decals added in 981ebf1, keeping the
older death-spray, spear-wound spurt, and "Blood & Gore" toggle:

- Delete blood_decals.gd + shader, the Gore autoload (gore.gd), and
  tests/blood_decals_test.gd
- Drop the Gore autoload and the Blood DP section
- Remove all Gore.splat() call sites (matador.gd, bear.gd, player.gd);
  the _blood_burst spray and _spawn_blood spurt stay
- game_shell no longer spawns a per-level decal pool
- Update level_switch test + run_tests.sh accordingly

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CmG3mQGVXZUPDVapmdbWZ1

debug_params.gd

@@ -306,18 +306,6 @@ func _register_all() -> void:
 	# it), so it can't be perma-stunlocked — it gets a window to commit an attack that then
 	# rides its hyper-armour. 0 = no poise (stun-locks under sustained fire).
 	_reg_f("Bear",     "bear_stagger_cd",      1.0,  0.0,   4.0, 0.05)
-	# ── Blood ─────────────────────────────────────────────────────────────────
-	# Persistent floor/wall splats (blood_decals.gd), fired via the Gore autoload and
-	# gated by the player's Settings.gore. blood_cap is the ring-buffer size: past it,
-	# new splats overwrite the oldest so fill/memory stay bounded. blood_scale is a
-	# global size multiplier over each hit's own size; satellites are extra droplets
-	# scattered per floor cluster; the wall fan casts blood_wall_rays outward and stains
-	# any wall within blood_wall_reach metres of the hit.
-	_reg_f("Blood",    "blood_cap",          192.0,  0.0, 512.0, 16.0)
-	_reg_f("Blood",    "blood_scale",          1.0,  0.1,   4.0, 0.05)
-	_reg_f("Blood",    "blood_satellites",     3.0,  0.0,   8.0, 1.0)
-	_reg_f("Blood",    "blood_wall_reach",     2.5,  0.0,   6.0, 0.1)
-	_reg_f("Blood",    "blood_wall_rays",      8.0,  0.0,  16.0, 1.0)
 	# ── Sword ─────────────────────────────────────────────────────────────────
 	# Local seating of the sword in the right hand (drawn / fighting).
 	# The blade model runs along its local +Z, but weapon_bone (like every rig bone)