feat(ui): 弹层进出场过渡 + 首屏暖深色英雄（P2-6/P4-6）

- useMountTransition hook（延迟卸载播放退场，尊重 reduced-motion）+ vitest
- Drawer 淡入+滑入进出场；focus/scroll-lock 仍由 open 驱动、focus 键 shouldRender 防丢首焦
- Toast 入场 toast-in 动画（motion-safe）
- P4-6 首屏零作品用 callout 暖深色编辑部英雄（对标 cta-band-dark，不干扰工作库）
  新增 callout/on-callout/on-callout-soft 双主题成对 token

apps/web/lib/ui/useMountTransition.test.ts

@@ -0,0 +1,53 @@
+// @vitest-environment jsdom
+import { act, renderHook } from "@testing-library/react";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { useMountTransition } from "./useMountTransition";
+
+beforeEach(() => {
+  vi.useFakeTimers();
+  // 让 rAF 同步执行，便于断言 isVisible 翻转。
+  vi.stubGlobal("requestAnimationFrame", (cb: FrameRequestCallback) => {
+    cb(0);
+    return 1;
+  });
+  vi.stubGlobal("cancelAnimationFrame", () => {});
+});
+
+afterEach(() => {
+  vi.useRealTimers();
+  vi.unstubAllGlobals();
+});
+
+describe("useMountTransition", () => {
+  it("renders nothing while closed", () => {
+    const { result } = renderHook(() => useMountTransition(false, 180));
+    expect(result.current.shouldRender).toBe(false);
+    expect(result.current.isVisible).toBe(false);
+  });
+
+  it("mounts and becomes visible when opened", () => {
+    const { result, rerender } = renderHook(
+      ({ open }) => useMountTransition(open, 180),
+      { initialProps: { open: false } },
+    );
+    act(() => rerender({ open: true }));
+    expect(result.current.shouldRender).toBe(true);
+    expect(result.current.isVisible).toBe(true);
+  });
+
+  it("keeps rendering during exit, then unmounts after the duration", () => {
+    const { result, rerender } = renderHook(
+      ({ open }) => useMountTransition(open, 180),
+      { initialProps: { open: true } },
+    );
+    act(() => rerender({ open: false }));
+    expect(result.current.isVisible).toBe(false);
+    expect(result.current.shouldRender).toBe(true);
+
+    act(() => {
+      vi.advanceTimersByTime(180);
+    });
+    expect(result.current.shouldRender).toBe(false);
+  });
+});