Remove UI multi cam setup

## Summary

Fixes #20.

- Reuse fighter animation scratch and output buffers across rollback frames.
- Select air-collision hits in one pass without candidate allocations or sorting.
- Index contiguous replay input frames directly and binary-search checksums.
- Add regression tests for buffer reuse and replay lookup/validation.

Reviewed-on: #53
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/menus/character_select/mod.rs

@@ -241,7 +241,7 @@ pub fn copy_cursor_transform_to_token(
     character_boxes: Query<(&CharacterBox, &ComputedNode, &UiGlobalTransform)>,
     match_config: Res<MenuMatchConfig>,
     cursors: Query<&UiGlobalTransform, With<FGMenuCursor>>,
-    cam: Single<&Camera, With<IsDefaultUiCamera>>,
+    cam: Single<&Camera>,
     ui_scale: Res<UiScale>,
 ) -> Result {
     let camera = cam.into_inner();

src/menus/cursor.rs

@@ -181,7 +181,7 @@ pub fn cursor_input(
 }
 
 pub fn update_cursor_transform(
-    camera: Single<&Camera, With<IsDefaultUiCamera>>,
+    camera: Single<&Camera>,
     query: Query<(&mut Node, &PointerLocation), With<FGMenuCursor>>,
     ui_scale: Res<UiScale>,
 ) {

src/menus/mod.rs

@@ -25,6 +25,8 @@ pub mod style;
 
 #[derive(Component, Clone, Default)]
 pub struct MenuMarker {}
+#[derive(Component, Clone, Default)]
+pub struct MenuCameraMarker {}
 
 pub struct MenuPlugin;
 
@@ -38,6 +40,7 @@ pub fn wrap_menu(menu: impl Scene) -> impl Scene {
     bsn! {
         #MenuRoot
         MenuMarker
+        Transform
         Node {
             width: percent(100),
             height: percent(100),
@@ -46,6 +49,11 @@ pub fn wrap_menu(menu: impl Scene) -> impl Scene {
             flex_direction: FlexDirection::Column,
         }
         Children [
+            (
+                #MenuCamera
+                Camera
+                Camera2d
+            ),
             (
                 #MenuContainer
                 Node {
@@ -65,15 +73,18 @@ pub fn wrap_menu(menu: impl Scene) -> impl Scene {
 
 pub fn despawn_menu(
     existing_menu: Option<Single<Entity, With<MenuMarker>>>,
+    existing_menu_camera: Option<Single<Entity, With<MenuCameraMarker>>>,
     mut commands: Commands,
 ) {
     if let Some(entity) = existing_menu {
         commands
             .entity(entity.into_inner())
-            .remove::<Camera2d>()
-            .remove::<Camera>()
             .despawn();
     }
+
+    if let Some(menu_cam) = existing_menu_camera {
+        commands.entity(*menu_cam).despawn();
+    }
 }
 
 pub fn spawn_menu(
@@ -84,8 +95,6 @@ pub fn spawn_menu(
     if let Some(entity) = existing_menu {
         commands
             .entity(entity.into_inner())
-            .remove::<Camera2d>()
-            .remove::<Camera>()
             .despawn();
     }
     commands.queue_spawn_scene(wrap_menu(menu));
@@ -113,16 +122,7 @@ impl Plugin for MenuPlugin {
     fn build(&self, app: &mut App) {
         app.add_systems(
             OnEnter(AppState::MainMenu),
-            (build_menu::<MainMenu>, |mut commands: Commands| {
-                commands.spawn((Camera2d, IsDefaultUiCamera));
-                commands.spawn((
-                    Camera2d,
-                    Camera {
-                        order: 1,
-                        ..default()
-                    },
-                ));
-            }),
+            build_menu::<MainMenu>,
         )
         .add_message::<character_select::PlayerSlotAssigned>()
         .init_resource::<navigation::UINavigationActionState>()