feat(gameplay): add scripted flight paths for special stage enemies

Add Lissajous and cubic Bezier path types for enemies on special stages
(every 3rd level). Path-following enemies spawn with ScriptedPath marker
and FollowingPath state, move along parametric curves, and despawn when
their path ends off-screen.

Key changes:
- New flight_paths module with pure path evaluation (Lissajous + Bezier)
- ScriptedPath marker component and FollowingPath EnemyState variant
- flight_patterns field on StageConfigurations for composable path data
- Special stage spawn branch in spawn_enemies() with stagger delays
- Path-following movement in move_enemies() with delay gating and despawn
- Formation complete early return for special stages
- Without<ScriptedPath> filter on attacking_query to prevent double-processing
- 13 new unit tests for path evaluation and data contracts

Refs: GAL-40

tests/special_stage.rs

@@ -110,7 +110,10 @@ fn for_stage_returns_normal_config_at_stage_4() {
 fn special_stage_has_full_formation() {
     let configs = StageConfigurations::default();
     let config = configs.for_stage(3);
-    assert_eq!(config.enemy_count, 32, "Special stage should have 32 enemies");
+    assert_eq!(
+        config.enemy_count, 32,
+        "Special stage should have 32 enemies"
+    );
     assert_eq!(
         config.formation_layout.positions.len(),
         32,