feat: implement textured line clear effects and refine UI alignment

- **Visual Effects**: Upgraded line clear particles to use the game's block texture instead of simple circles, matching the reference web game's aesthetic.
- **Particle Physics**: Tuned particle velocity, gravity, and fade rates for a more dynamic explosion effect.
- **Rendering Integration**: Updated [main.cpp](cci:7://file:///d:/Sites/Work/tetris/src/main.cpp:0:0-0:0) and `GameRenderer` to pass the block texture to the effect system and correctly trigger animations upon line completion.
- **Menu UI**: Fixed [MenuState](cci:1://file:///d:/Sites/Work/tetris/src/states/MenuState.cpp:19:0-19:55) layout calculations to use fixed logical dimensions (1200x1000), ensuring consistent centering and alignment of the logo, buttons, and settings icon across different window sizes.
- **Code Cleanup**: Refactored `PlayingState` to delegate effect triggering to the rendering layer where correct screen coordinates are available.

src/graphics/effects/Starfield.h

@@ -0,0 +1,15 @@
+// Starfield.h - Procedural starfield background effect
+#pragma once
+#include <vector>
+struct SDL_Renderer; // fwd
+
+class Starfield {
+public:
+    void init(int count, int w, int h);
+    void update(float dt, int w, int h);
+    void draw(SDL_Renderer* r) const;
+private:
+    struct Star { float x,y,z,speed; };
+    std::vector<Star> stars;
+    int lastW{0}, lastH{0};
+};