feat(viewer): UI-02 dark immersive photo viewer with thumbnail strip

V04 (方案 §5)：PhotoLightbox 模板重构为深色沉浸布局——顶栏（关闭/位置
计数/⋯ 减少动画菜单）+ 舞台（contain 大图 + 边缘 ‹› + 粒子/互动占位层）+
缩略图条 + 底部操作栏；业务逻辑（序列导航/缩放手势/签名刷新/下载/点赞）
原样保留。

- 新增 viewer/position.ts：§5.2 位置计数真实回退（solo→照片预览；无
  total 未到末页→已加载 N 张；全部加载→i/n；不伪造总数）
- 新增 ThumbnailStrip：当前 ±3 窗口（≤7 项）、主色 2px 描边、thumb 变体、
  滚入可见（遵守减少动画）、点击选择不新增历史
- 新增 PhotoActionBar：Like（coral 心形+计数+连续点赞提示）/Share/
  Download 均分大触控；下载关闭整项移除；原图二级菜单（▾ + 长按）
- 模态可用性：body 滚动锁、焦点进入/困住/归还触发元素、Esc 先收菜单、
  菜单内左右键不抢占、dvh + 安全区、chrome 区手势/滚轮隔离
- 分享 V04 最小实现（复制当前深链，support/clipboard 从 AlbumHeader
  提取共用）；navigator.share 编排属 Task 5
- zh-CN/en 新词条；vitest 新增 23 例（位置回退/缩略图/操作栏/焦点/滚锁）

Co-Authored-By: Claude Code <noreply@anthropic.com>

apps/viewer/src/__tests__/download.spec.ts

@@ -187,16 +187,16 @@ describe('photo download (P4a Task 4)', () => {
     // on/off：单按钮，无 caret/菜单。
     const browseOnly = mountLightbox(makeAlbum());
     await flushPromises();
-    expect(browseOnly.find('.control.download').exists()).toBe(true);
-    expect(browseOnly.find('.control.download-caret').exists()).toBe(false);
+    expect(browseOnly.find('.download-main').exists()).toBe(true);
+    expect(browseOnly.find('.download-caret').exists()).toBe(false);
 
     // on/on：分体按钮（caret 出现，菜单默认收起）。
     const split = mountLightbox(makeAlbum({ originalDownloadEnabled: true }));
     await flushPromises();
-    expect(split.find('.control.download-caret').exists()).toBe(true);
+    expect(split.find('.download-caret').exists()).toBe(true);
     expect(split.find('.download-menu').exists()).toBe(false);
     // 主按钮 aria 展开 = false。
-    expect(split.find('.control.download-caret').attributes('aria-expanded')).toBe('false');
+    expect(split.find('.download-caret').attributes('aria-expanded')).toBe('false');
   });
 
   it('split menu offers both variants; picking original requests the original endpoint', async () => {
@@ -204,9 +204,9 @@ describe('photo download (P4a Task 4)', () => {
     const wrapper = mountLightbox(makeAlbum({ originalDownloadEnabled: true }));
     await flushPromises();
 
-    await wrapper.find('.control.download-caret').trigger('click');
+    await wrapper.find('.download-caret').trigger('click');
     const items = wrapper.findAll('.download-menu button');
-    expect(items.map((item) => item.text())).toEqual(['下载图片', '下载原图']);
+    expect(items.map((item) => item.text())).toEqual(['浏览图', '原图']);
 
     await items[1]!.trigger('click');
     await flushPromises();
@@ -224,7 +224,7 @@ describe('photo download (P4a Task 4)', () => {
     const wrapper = mountLightbox(makeAlbum());
     await flushPromises();
 
-    await wrapper.find('.control.download').trigger('click');
+    await wrapper.find('.download-main').trigger('click');
     await flushPromises();
     expect(mockedGetPhotoDownload).toHaveBeenCalledTimes(2);
     expect(mockedGetPhotoDownload).toHaveBeenCalledWith('tok-dl', 'p1', 'browse');
@@ -236,7 +236,7 @@ describe('photo download (P4a Task 4)', () => {
     const wrapper = mountLightbox(makeAlbum());
     await flushPromises();
 
-    await wrapper.find('.control.download').trigger('click');
+    await wrapper.find('.download-main').trigger('click');
     await flushPromises();
     expect(mockedGetPhotoDownload).toHaveBeenCalledTimes(1);
     expect(openSpy).toHaveBeenCalledWith('http://img.test/p1-browse.jpg', '_blank', 'noopener,noreferrer');
@@ -245,7 +245,7 @@ describe('photo download (P4a Task 4)', () => {
     // 端点失败（网络/403 等）→ 失败提示可再见（再次点击重试）。
     openSpy.mockClear();
     mockedGetPhotoDownload.mockReset().mockRejectedValue(new Error('boom'));
-    await wrapper.find('.control.download').trigger('click');
+    await wrapper.find('.download-main').trigger('click');
     await flushPromises();
     expect(wrapper.find('.download-failed[role="alert"]').text()).toContain('下载失败');
     expect(openSpy).not.toHaveBeenCalled();
@@ -259,7 +259,7 @@ describe('photo download (P4a Task 4)', () => {
     const wrapper = mountLightbox(makeAlbum());
     await flushPromises();
 
-    await wrapper.find('.control.download').trigger('click');
+    await wrapper.find('.download-main').trigger('click');
     await flushPromises();
     expect(wrapper.find('.download-failed[role="alert"]').text()).toContain('该相册未开放下载');
     expect(wrapper.find('.download-failed').text()).not.toContain('下载失败');
@@ -270,7 +270,7 @@ describe('photo download (P4a Task 4)', () => {
     const wrapper = mountLightbox(makeAlbum());
     await flushPromises();
 
-    await wrapper.find('.control.download').trigger('click');
+    await wrapper.find('.download-main').trigger('click');
     await flushPromises();
     expect(wrapper.find('.wechat-guide[role="dialog"]').exists()).toBe(true);
     expect(wrapper.find('.wechat-guide h2').text()).toBe('保存图片指引');
@@ -289,7 +289,7 @@ describe('photo download (P4a Task 4)', () => {
     const wrapper = mountLightbox(makeAlbum());
     await flushPromises();
 
-    await wrapper.find('.control.download').trigger('click');
+    await wrapper.find('.download-main').trigger('click');
     await wrapper.find('.guide-copy').trigger('click');
     await flushPromises();
     expect(writeText).toHaveBeenCalledWith(window.location.href);