Add overlay gamepad support for keyboard-only mode (#17)

src/renderer/yomitan-display-scroll.test.ts

@@ -0,0 +1,24 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+// @ts-expect-error Vendor Yomitan modules are JS-only in this repo.
+import { Display } from '../../vendor/subminer-yomitan/ext/js/display/display.js';
+
+test('yomitan display scroll bridge uses popup scroll container instead of window scroll', () => {
+  let scrolledTo: { x: number; y: number } | null = null;
+  const result = Display.prototype._onMessageScrollBy.call(
+    {
+      _windowScroll: {
+        x: 24,
+        y: 80,
+        to(x: number, y: number) {
+          scrolledTo = { x, y };
+        },
+      },
+    },
+    { deltaX: 12, deltaY: -20 },
+  );
+
+  assert.equal(result, true);
+  assert.deepEqual(scrolledTo, { x: 36, y: 60 });
+});