feat(starfield): capa parallax al fons del playfield amb tint blanc-cyan

source/game/scenes/game_scene.cpp

@@ -30,6 +30,7 @@ GameScene::GameScene(SDLManager& sdl, SceneContext& context)
       floating_score_manager_(sdl.getRenderer()),
       trail_manager_(sdl.getRenderer()),
       text_(sdl.getRenderer()),
+      starfield_parallax_(sdl.getRenderer()),
       playfield_(sdl.getRenderer()),
       border_(sdl.getRenderer()) {
     // Recuperar configuración de match des del context
@@ -213,6 +214,9 @@ void GameScene::stepPhysics(float delta_time) {
         bullet.postUpdate(delta_time);
     }
     trail_manager_.update(delta_time, ships_);
+    // De moment world_velocity = {0, 0} → estrelles quietes; al ser-hi l'estat
+    // del wraparound es resol normalment quan activem el moviment.
+    starfield_parallax_.update(delta_time, Vec2{.x = 0.0F, .y = 0.0F});
     playfield_.update(delta_time);
     border_.update(delta_time);
 
@@ -569,6 +573,7 @@ void GameScene::drawActiveShipsAlive() const {
 }
 
 void GameScene::drawContinueState() {
+    starfield_parallax_.draw();
     border_.draw();
     drawEnemies();
     drawBullets();
@@ -580,6 +585,7 @@ void GameScene::drawContinueState() {
 }
 
 void GameScene::drawGameOverState() {
+    starfield_parallax_.draw();
     border_.draw();
     drawEnemies();
     drawBullets();
@@ -625,6 +631,8 @@ void GameScene::drawInitHudState() {
         Defaults::Game::INIT_HUD_SHIP2_RATIO_INIT,
         Defaults::Game::INIT_HUD_SHIP2_RATIO_END);
 
+    // Capa de fons més profunda: estrelles 2D (apareixen senceres des del frame 0).
+    starfield_parallax_.draw();
     // Graella de fons al darrere (timer intern propi, cobreix tot l'INIT_HUD).
     playfield_.draw();
 
@@ -650,6 +658,7 @@ void GameScene::drawInitHudState() {
 }
 
 void GameScene::drawLevelStartState() {
+    starfield_parallax_.draw();
     playfield_.draw();
     border_.draw();
     trail_manager_.draw();
@@ -663,6 +672,7 @@ void GameScene::drawLevelStartState() {
 }
 
 void GameScene::drawPlayingState() {
+    starfield_parallax_.draw();
     playfield_.draw();
     border_.draw();
     trail_manager_.draw();
@@ -676,6 +686,7 @@ void GameScene::drawPlayingState() {
 }
 
 void GameScene::drawLevelCompletedState() {
+    starfield_parallax_.draw();
     playfield_.draw();
     border_.draw();
     trail_manager_.draw();