Wave escalation and the Snippest boss

Escalation (EnemySpawner exports, all tunable):
- Wave size grows +1 enemy per wave, capped at 20
- Enemy health +15% and damage +10% per wave, applied identically on
  every peer via the spawn RPC before _ready (so hitbox stats and
  current_health pick them up)

Boss milestone every 5th wave: the Snippest - the basic lobster at
5x scale and 5x combat stats (50 HP, 25 damage, 5x knockback and
reach). Movement deliberately not 5x (1.2x - it lumbers). Pays 250
gold and always drops a health orb. Wave escalation multipliers stack
on top, so later bosses keep scaling.

Boss scene instances basic_enemy.tscn with the BossLobster script;
visual/collision children are scaled uniformly in code (not the
CharacterBody3D root, not shared shape resources).

level/scripts/boss_lobster.gd

@@ -0,0 +1,35 @@
+extends BasicEnemy
+class_name BossLobster
+## The Snippest itself: a lobster five times the size with five times the stats.
+## Spawned by the EnemySpawner on boss milestone waves.
+
+const BOSS_MULTIPLIER := 5.0
+
+func _ready():
+	# 5x combat stats - applied BEFORE super._ready() so the hitbox
+	# picks them up via set_stats(attack_damage, attack_knockback)
+	max_health *= BOSS_MULTIPLIER
+	attack_damage *= BOSS_MULTIPLIER
+	attack_knockback *= BOSS_MULTIPLIER
+	attack_range *= BOSS_MULTIPLIER  # A 5x lobster has 5x reach
+
+	# Deliberately NOT 5x: movement (17.5 speed would be inescapable).
+	# Big things lumber. Tune here if the boss should be faster.
+	move_speed *= 1.2
+
+	# Boss rewards: jackpot gold, guaranteed health orb
+	gold_reward = 250
+	health_orb_drop_chance = 1.0
+
+	super._ready()
+
+	_apply_boss_scale()
+
+## Uniformly scale the visual and collision children 5x around the root.
+## Child-node scaling (not root CharacterBody3D scale, not shared shape
+## resources) keeps physics sane and other lobsters unaffected.
+func _apply_boss_scale():
+	for child_name in ["Mesh", "CollisionShape3D", "HurtBox", "HitBox"]:
+		var child = get_node_or_null(child_name)
+		if child:
+			child.transform = child.transform.scaled(Vector3.ONE * BOSS_MULTIPLIER)