New mechanics: coins + magnet + Gas Limit shield

Coins: collectible  dropped in clusters (lines/arcs) above platforms; collected on overlap, banked into a persistent wallet at game over, shown in HUD and on the GameOver screen. Magnet power-up pulls nearby coins toward the player for 6s (HUD duration bar). Gas Limit shield power-up grants a cyan aura that absorbs one enemy hit instead of dying, then breaks. New procedural textures (coin/magnet/shield), spawn weights, durations, sound, and stats (coins collected, GWEI wallet) wired through ScoreManager/StatsManager/Settings. Verified via in-browser sim: coins spawn, magnet pull 100px to 10px, collect increments GWEI, shield absorbs a hit (no game over) while no shield = death.

src/entities/Magnet.js

@@ -0,0 +1,33 @@
+import { Physics } from 'phaser';
+
+export class Magnet extends Physics.Arcade.Sprite {
+  constructor(scene, x, y) {
+    super(scene, x, y, 'magnet');
+    scene.add.existing(this);
+    scene.physics.add.existing(this, true);
+
+    this.setScale(0.8);
+    this.body.setSize(this.width * 0.8, this.height * 0.8);
+    this.body.setOffset(this.width * 0.1, this.height * 0.1);
+    this.consumed = false;
+
+    this.floatTween = scene.tweens.add({
+      targets: this, y: y - 6, duration: 700, yoyo: true, repeat: -1, ease: 'Sine.easeInOut',
+    });
+  }
+
+  onPlayerTouch(player) {
+    if (this.consumed) return false;
+    this.consumed = true;
+    this.body.enable = false;
+    this.setVisible(false);
+    player.startMagnet();
+    this.destroy();
+    return true;
+  }
+
+  destroy(fromScene) {
+    if (this.floatTween) { this.floatTween.stop(); this.floatTween = null; }
+    super.destroy(fromScene);
+  }
+}