test(frontend): sample component tests for button/dialog/theme-toggle (B2)

frontend/test/setup.ts

@@ -19,3 +19,27 @@ Element.prototype.scrollIntoView ??= function scrollIntoView() {};
 Element.prototype.hasPointerCapture ??= (() => false) as never;
 Element.prototype.setPointerCapture ??= (() => {}) as never;
 Element.prototype.releasePointerCapture ??= (() => {}) as never;
+
+// jsdom 未实现 matchMedia（theme.tsx 按 prefers-color-scheme 求值）：EventTarget 基类覆盖
+// addEventListener/removeEventListener，addListener/removeListener 是旧版 legacy API 兼容面。
+class MediaQueryListStub extends EventTarget {
+  media: string;
+  matches: boolean;
+  onchange: ((this: MediaQueryList, ev: MediaQueryListEvent) => unknown) | null = null;
+
+  constructor(media: string) {
+    super();
+    this.media = media;
+    this.matches = false;
+  }
+
+  addListener(listener: (this: MediaQueryList, ev: MediaQueryListEvent) => unknown) {
+    this.addEventListener("change", listener as EventListener);
+  }
+
+  removeListener(listener: (this: MediaQueryList, ev: MediaQueryListEvent) => unknown) {
+    this.removeEventListener("change", listener as EventListener);
+  }
+}
+
+globalThis.matchMedia ??= ((media: string) => new MediaQueryListStub(media)) as unknown as typeof matchMedia;