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.

tests/test_gas_bomber.gd

@@ -107,16 +107,19 @@ func _process(delta: float) -> bool:
 			if main.get_node("Camera2D").zoom.x >= original_zoom:
 				return _fail_now("long aim did not zoom out")
 
+			# speed is set AFTER add_child(): _ready() copies it from the
+			# enemy's definition, which would otherwise clobber a
+			# pre-add_child override the instant the enemy entered the tree.
 			for offset in [Vector2(-60, 0), Vector2(70, 35)]:
 				var enemy: Node = load("res://Enemy.tscn").instantiate()
 				enemy.position = skill.aim_target + offset
-				enemy.speed = 0.0
 				main.add_child(enemy)
+				enemy.speed = 0.0
 				inside_enemies.append(enemy)
 			outside_enemy = load("res://Enemy.tscn").instantiate()
 			outside_enemy.position = skill.aim_target + Vector2(GasBombController.AOE_RADIUS + 80.0, 0)
-			outside_enemy.speed = 0.0
 			main.add_child(outside_enemy)
+			outside_enemy.speed = 0.0
 
 			var release := InputEventScreenTouch.new()
 			release.index = 7