feat: player entity with WASD movement, tile collision, camera follow (Phase 4.1)

Player spawns at walkable tile near map center. WASD controls movement
(150px/s, normalized diagonal). Tile collision with wall-sliding prevents
walking through acid pools, crystals, geysers. Camera follows player with
smooth lerp. 39 new tests (134 total).

Co-authored-by: Cursor <cursoragent@cursor.com>

src/world/camera.ts

@@ -67,3 +67,29 @@ export function updateCamera(
   if (keys.up.isDown) camera.scrollY -= speed * dt;
   if (keys.down.isDown) camera.scrollY += speed * dt;
 }
+
+/**
+ * Set up camera for player-follow mode.
+ * No WASD movement — camera follows the player entity.
+ * Zoom via mouse wheel, bounds clamped to world size.
+ */
+export function setupPlayerCamera(
+  scene: Phaser.Scene,
+  worldPixelWidth: number,
+  worldPixelHeight: number,
+): void {
+  const camera = scene.cameras.main;
+  camera.setBounds(0, 0, worldPixelWidth, worldPixelHeight);
+  camera.setZoom(2); // closer view for gameplay
+
+  // Mouse wheel zoom (0.5x – 3x)
+  scene.input.on('wheel', (
+    _pointer: unknown,
+    _gameObjects: unknown,
+    _deltaX: number,
+    deltaY: number,
+  ) => {
+    const newZoom = Phaser.Math.Clamp(camera.zoom - deltaY * 0.001, 0.5, 3);
+    camera.setZoom(newZoom);
+  });
+}