tweak(playfield): rejilla violeta synthwave + brillos +5%; starfield unificat al color del títol

source/core/graphics/playfield.cpp

@@ -290,7 +290,9 @@ namespace Graphics {
                 static_cast<int>(START_Y),
                 static_cast<int>(END_X),
                 static_cast<int>(END_Y),
-                line.brightness);
+                line.brightness,
+                0.0F,
+                Defaults::Playfield::GRID_COLOR);
             // Cap brillant mentre creix.
             if (P < 1.0F) {
                 const float LENGTH = std::sqrt((DX * DX) + (DY * DY));
@@ -302,7 +304,9 @@ namespace Graphics {
                         static_cast<int>(START_Y + (DY * HEAD_T)),
                         static_cast<int>(END_X),
                         static_cast<int>(END_Y),
-                        Defaults::Playfield::HEAD_BRIGHTNESS);
+                        Defaults::Playfield::HEAD_BRIGHTNESS,
+                        0.0F,
+                        Defaults::Playfield::GRID_COLOR);
                 }
             }
             return;
@@ -329,7 +333,9 @@ namespace Graphics {
                 static_cast<int>(prev_y),
                 static_cast<int>(NX),
                 static_cast<int>(NY),
-                line.brightness);
+                line.brightness,
+                0.0F,
+                Defaults::Playfield::GRID_COLOR);
             prev_x = NX;
             prev_y = NY;
         }

source/core/graphics/starfield_parallax.cpp

@@ -31,20 +31,15 @@ namespace Graphics {
         const float MIN_Y = zona.y;
         const float MAX_Y = zona.y + zona.h;
 
-        // Tint aleatori entre blanc (255,255,255) i cyan (0,255,255) per estrella.
-        // T ∈ [0,1]: 0 → blanc; 1 → cyan. R = 255·(1-T), G=B=255.
+        // Color únic per a totes les estrelles: el mateix blanc-blau gel
+        // del starfield del títol (Defaults::Title::Colors::STARFIELD).
         const auto FILL_LAYER = [&](int layer, int count, int& idx) {
             for (int i = 0; i < count; i++) {
-                const float T = randUniform(0.0F, 1.0F);
                 stars_[idx++] = Star{
                     .x = randUniform(MIN_X, MAX_X),
                     .y = randUniform(MIN_Y, MAX_Y),
                     .layer = layer,
-                    .color = SDL_Color{
-                        .r = static_cast<Uint8>(255.0F * (1.0F - T)),
-                        .g = 255,
-                        .b = 255,
-                        .a = 255}};
+                    .color = Defaults::Title::Colors::STARFIELD};
             }
         };