feat(biome): abyssal bioluminescent + glow blocks + abyssal jellyfish + particles

- BlockDatabase: GLOW_CORAL_CYAN(10), GLOW_CORAL_VIOLET(11), LAVA_VENT(12) with emission data
- WorldGenerator: abyssal blocks at y<-40 (cyan 4%, violet 1%, vent 0.5% via 3D noise)
- Chunk.gd: multi-surface mesh (solid + 3 emissive surfaces with StandardMaterial3D emission)
- MobSpawner: abyssal jellyfish spawn when player y<-30, max 8
- AbyssalJellyfish: cyan fluo, slower, double damage (10), bioluminescent flash on attack
- BioluminescentParticles: 200 cyan-green particles follow player, only emit in abyss

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/mobs/MobSpawner.gd

@@ -6,10 +6,12 @@ extends Node3D
 @export var max_fish_schools: int = 3
 @export var max_jellyfish: int = 5
 @export var max_sharks: int = 1
+@export var abyssal_jellyfish_max: int = 8
 
 const FISH_SCHOOL_SCENE := "res://scenes/mobs/FishSchool.tscn"
 const JELLYFISH_SCENE := "res://scenes/mobs/Jellyfish.tscn"
 const SHARK_SCENE := "res://scenes/mobs/Shark.tscn"
+const ABYSSAL_JELLYFISH_SCENE := "res://scenes/mobs/AbyssalJellyfish.tscn"
 
 var _player_node: CharacterBody3D = null
 var _chunk_manager: Node = null
@@ -19,6 +21,7 @@ const SPAWN_INTERVAL: float = 5.0
 var _fish_schools: Array[Node3D] = []
 var _jellyfish_list: Array[Node3D] = []
 var _sharks: Array[Node3D] = []
+var _abyssal_jellyfish_list: Array[Node3D] = []
 
 
 func _ready() -> void:
@@ -67,6 +70,7 @@ func _tick_spawner() -> void:
 	_cull_array(_fish_schools, player_pos)
 	_cull_array(_jellyfish_list, player_pos)
 	_cull_array(_sharks, player_pos)
+	_cull_array(_abyssal_jellyfish_list, player_pos)
 
 	# --- Spawn fish schools ---
 	while _fish_schools.size() < max_fish_schools:
@@ -100,6 +104,18 @@ func _tick_spawner() -> void:
 			else:
 				break
 
+	# --- Spawn abyssal jellyfish only in deep zone ---
+	if player_pos.y < -30.0:
+		while _abyssal_jellyfish_list.size() < abyssal_jellyfish_max:
+			var pos: Vector3 = _random_abyss_spawn_pos(player_pos)
+			if _is_valid_spawn(pos):
+				var inst: Node3D = _load_and_instantiate(ABYSSAL_JELLYFISH_SCENE, pos)
+				if inst != null:
+					_connect_mob_signal(inst)
+					_abyssal_jellyfish_list.append(inst)
+				else:
+					break
+
 
 func _cull_array(arr: Array[Node3D], player_pos: Vector3) -> void:
 	var i: int = arr.size() - 1
@@ -123,6 +139,18 @@ func _random_spawn_pos(player_pos: Vector3) -> Vector3:
 	)
 
 
+func _random_abyss_spawn_pos(player_pos: Vector3) -> Vector3:
+	var angle: float = randf_range(0.0, TAU)
+	var dist: float = randf_range(10.0, spawn_radius)
+	var depth: float = randf_range(player_pos.y - 15.0, player_pos.y + 5.0)
+	depth = min(depth, -30.0)
+	return Vector3(
+		player_pos.x + cos(angle) * dist,
+		depth,
+		player_pos.z + sin(angle) * dist
+	)
+
+
 func _is_valid_spawn(pos: Vector3) -> bool:
 	if _chunk_manager == null:
 		return true