Add chase drift, main/pause menus, and unlockable skins

Zones 20 and 40 now push everything rightward for the first 20
seconds of their chase, forcing the player to tap left to stay on
screen. Added a main menu (new game / continue / skins), an in-game
pause menu, and a skins system that unlocks permanent stat bonuses
(speed, damage, HP, crystal/dark-matter/droid multipliers) as the
player's max zone reached increases.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D5SuZW1XGCkahPX7cHMoRP

src/components/PauseMenu.tsx

@@ -0,0 +1,28 @@
+export function PauseMenu({
+  onResume,
+  onSkins,
+  onMainMenu,
+}: {
+  onResume: () => void;
+  onSkins: () => void;
+  onMainMenu: () => void;
+}) {
+  return (
+    <div className="menu-overlay">
+      <div className="menu-panel">
+        <div className="menu-title">Пауза</div>
+        <div className="menu-buttons">
+          <button type="button" className="menu-btn menu-btn--primary" onClick={onResume}>
+            Продолжить
+          </button>
+          <button type="button" className="menu-btn" onClick={onSkins}>
+            Скины
+          </button>
+          <button type="button" className="menu-btn" onClick={onMainMenu}>
+            Главное меню
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}