feat(viewer): UI-02 visual foundation, top bar and album info

V01+V02 (Task 2 of the UI-02 viewer redesign plan):

- viewer-tokens.css: UI-02 §3.1 design tokens scoped to .viewer-shell
  (never :root), so embed routes consume none of them
- App.vue: normal routes get a sticky white top bar (PhotoLive brand +
  compact locale switcher + lightweight "..." menu holding the
  reduce-motion toggle); global 16px content padding removed so banner
  and photos run edge-to-edge; embed shell branch untouched
- LocaleSwitcher: compact "EN/中文 + caret" trigger with a proper menu
  (current language checked), 44px touch target, Escape/outside close
- AlbumHeader (new): banner (2.4:1 mobile, 320px desktop cap,
  object-fit contain, collapses on missing/failed), 2-line expandable
  title + share button (clipboard copy with selectable-text fallback),
  3-line expandable pre-line description, meta row (Intl-formatted
  view count with em-dash fallback for unknown, album-timezone dates
  with full range on title, venue), Latest/Popular 44px tabs and
  category pills from the API with horizontal scroll + overflow fade
- ActivityPage: delegates the info area to AlbumHeader; sequence
  reset/sort-lock/category-by-id semantics unchanged; desktop content
  capped at 1120px
- i18n: viewer.* strings (brand/share/views/readMore/latest/popular/
  allCategories/noPhotos/newPhotos/reduceMotion/settings) in zh-CN+en
- tests: viewer-shell (token source + normal/embed isolation) and
  album-header (8 cases) specs; activity/i18n specs updated for the
  menu switcher and the em-dash unknown view count; e2e selectors
  refreshed

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

apps/viewer/src/__tests__/i18n.spec.ts

@@ -28,15 +28,27 @@ describe('viewer i18n', () => {
     expect(wrapper.text()).toContain('打开相册链接即可观看');
     expect(document.title).toBe('现场相册');
 
-    await wrapper.find('button.locale-switcher').trigger('click');
+    // UI-02 V01 紧凑语言控件：展开菜单 → 选择 English。
+    await wrapper.find('.locale-trigger').trigger('click');
+    await nextTick();
+    const english = wrapper.findAll('.locale-option').find((btn) => btn.text() === 'English');
+    expect(english).toBeDefined();
+    await english!.trigger('click');
     await nextTick();
     expect(wrapper.text()).toContain('Open an album link to start viewing');
     expect(document.title).toBe('Live Gallery');
     expect(document.documentElement.getAttribute('lang')).toBe('en');
     expect(localStorage.getItem(LOCALE_STORAGE_KEY)).toBe('en');
 
-    // 切回 zh-CN 同样生效
-    await wrapper.find('button.locale-switcher').trigger('click');
+    // 切回 zh-CN 同样生效（菜单内当前语言 English 为勾选态）。
+    await wrapper.find('.locale-trigger').trigger('click');
+    await nextTick();
+    const options = wrapper.findAll('.locale-option');
+    const englishNow = options.find((btn) => btn.text() === 'English');
+    expect(englishNow!.attributes('aria-checked')).toBe('true');
+    const chinese = options.find((btn) => btn.text() === '中文');
+    expect(chinese!.attributes('aria-checked')).toBe('false');
+    await chinese!.trigger('click');
     await nextTick();
     expect(wrapper.text()).toContain('打开相册链接即可观看');
     expect(localStorage.getItem(LOCALE_STORAGE_KEY)).toBe('zh-CN');