Add standoff sniper enemy (#45)

EnemyStandoffComponent holds a preferred distance from the nearest
player ship instead of ramming (advance beyond it, retreat inside
retreat_range_factor of it, drift laterally in the comfortable band
between) - never paired with a pursuit component. EnemyRangedWeaponComponent
mirrors VesselWeaponComponent for an enemy: fires an EnemyProjectile
aimed at the target's CURRENT position rather than led, so a moving
ship can dodge it (projectile_speed 260 vs the interceptor's 460
max_speed). Registered in EnemyDefinitions so it's placeable from a
planet setup by enemy_id.

test_sniper_enemy.gd went through a few iterations to get its own
timing right: physics ticks can run ahead of a SceneTree test's own
_process() clock under this device's load, so the cooldown-violation
check reads the component's own fire_timer directly (a rising value
means it refired) instead of comparing projectile counts against a
wall-clock wait, and manually repositioned ships need their
move_target re-pinned or Ship's own steering silently drives them back
to the stale target.

Part of the #40 conquest-mechanic breakdown.

EnemyStandoffComponent.gd

@@ -0,0 +1,58 @@
+class_name EnemyStandoffComponent
+extends Node
+
+# Holds a preferred distance from the nearest player ship instead of
+# ramming: advances when too far, retreats when too close, drifts
+# laterally in the comfortable band between so it still reads as alive
+# rather than frozen. Never pair with a pursuit component on the same
+# enemy - the two would fight over velocity every tick.
+
+var capability_id: String = "standoff"
+
+@export var preferred_range: float = 620.0
+@export var retreat_range_factor: float = 0.75
+
+var velocity: Vector2 = Vector2.ZERO
+
+
+func tick(delta: float) -> void:
+	var enemy: Node2D = get_parent()
+	var target: Node2D = _nearest_ship(enemy)
+	if target == null:
+		return
+	var to_target: Vector2 = target.position - enemy.position
+	var distance: float = to_target.length()
+	if distance < 1.0:
+		return
+	var direction: Vector2 = to_target / distance
+	var retreat_range: float = preferred_range * retreat_range_factor
+
+	var desired_velocity: Vector2
+	if distance > preferred_range:
+		desired_velocity = direction * enemy.speed
+	elif distance < retreat_range:
+		desired_velocity = -direction * enemy.speed
+	else:
+		var lateral: Vector2 = Vector2(-direction.y, direction.x)
+		desired_velocity = lateral * enemy.speed * 0.5
+
+	velocity = velocity.move_toward(desired_velocity, enemy.acceleration * delta)
+	enemy.position += velocity * delta
+
+	if velocity.length() > 5.0:
+		var target_angle: float = velocity.angle() + PI / 2.0
+		enemy.rotation = lerp_angle(enemy.rotation, target_angle, enemy.rotation_speed * delta)
+
+
+func _nearest_ship(enemy: Node2D) -> Node2D:
+	var fleet: Node2D = get_tree().get_first_node_in_group("player_fleet")
+	if fleet == null or fleet.ships.is_empty():
+		return null
+	var nearest: Node2D = fleet.ships[0]
+	var best_dist: float = enemy.position.distance_to(nearest.position)
+	for ship in fleet.ships:
+		var d: float = enemy.position.distance_to(ship.position)
+		if d < best_dist:
+			best_dist = d
+			nearest = ship
+	return nearest