Add enemy foundation: definitions, components, ranged damage (#44)

Enemy.gd now resolves stats/hull/color from EnemyDefinition resources
and composes behaviour from capability components (EnemyPursuitComponent
holds today's chase-the-nearest-ship logic), the same shape Ship.gd
already uses for vessels. Fleet lookups go through a "player_fleet"
group instead of a hardcoded ../Fleet sibling path, so an enemy parented
anywhere (e.g. under a planet surface's SurfaceFeatures) still finds it.

Also closes a real gap: enemies previously had no way to damage the
fleet at range at all (Ship only reacted to physical contact,
Projectile.gd was player-only). Ship.take_damage() is now a proper
entry point - contact damage routes through it unchanged - and
EnemyProjectile lets an enemy component fire at player_ships. Both
ranged enemy archetypes in #45/#46 build on this.

Part of the #40 conquest-mechanic breakdown.

Ship.gd

@@ -115,17 +115,27 @@ func _physics_process(delta: float) -> void:
 		rotation = lerp_angle(rotation, target_angle, rotation_speed * delta)
 
 
-func _on_area_entered(area: Area2D) -> void:
-	if not (area.is_in_group("enemies") or area.is_in_group("asteroids")):
-		return
+func take_damage(_amount: int) -> bool:
+	# Ships have no hit points - any unabsorbed hit is lethal. A shield
+	# charge absorbs a hit entirely regardless of its amount, matching
+	# VesselShieldComponent's existing all-or-nothing semantics; `_amount`
+	# is accepted (not `int`-clamped away) so callers like EnemyProjectile
+	# have a normal damage parameter to pass even though it isn't graded here.
 	for child in get_children():
 		if child.has_method("absorb_hit") and child.absorb_hit():
-			if area.is_in_group("asteroids") and is_instance_valid(area):
-				area.queue_free()
-			return
+			return true
 	ShipExplosionVFX.spawn(get_tree().root, position)
 	destroyed.emit()
 	queue_free()
+	return false
+
+
+func _on_area_entered(area: Area2D) -> void:
+	if not (area.is_in_group("enemies") or area.is_in_group("asteroids")):
+		return
+	var absorbed: bool = take_damage(1)
+	if absorbed and area.is_in_group("asteroids") and is_instance_valid(area):
+		area.queue_free()
 
 
 func _draw() -> void: