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.

EnemyDefinitions.gd

@@ -0,0 +1,19 @@
+class_name EnemyDefinitions
+extends RefCounted
+
+const DEFAULT_ID: String = "chaser"
+const ORDER: PackedStringArray = ["chaser"]
+const DEFINITIONS: Dictionary = {
+	"chaser": preload("res://ChaserEnemyDefinition.tres"),
+}
+
+
+static func get_definition(enemy_id: String) -> Resource:
+	return DEFINITIONS.get(enemy_id, DEFINITIONS[DEFAULT_ID])
+
+
+static func all() -> Array:
+	var result: Array = []
+	for enemy_id in ORDER:
+		result.append(DEFINITIONS[enemy_id])
+	return result