feat: implement Suika Game (Watermelon Game)

Browser-based physics puzzle game where players drop fruits that merge
into larger fruits on collision, using Matter.js for 2D physics and
Canvas2D for rendering. Includes 11-fruit progression chain, scoring,
game-over detection, mouse/touch input, and Vitest test suite.

src/style.css

@@ -0,0 +1,29 @@
+* {
+  margin: 0;
+  padding: 0;
+  box-sizing: border-box;
+}
+
+body {
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  min-height: 100vh;
+  background: #2C3E50;
+  font-family: sans-serif;
+  overflow: hidden;
+}
+
+#app {
+  display: flex;
+  justify-content: center;
+  align-items: center;
+}
+
+#game-canvas {
+  border-radius: 8px;
+  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
+  max-width: 100vw;
+  max-height: 100vh;
+  touch-action: none;
+}