feat(viewer): share sheet with QR code + link + copy (replaces inline toast, App-style)

- ShareSheet.vue: bottom sheet (mobile) / centered card (desktop) — QR canvas (qrcode dep), selectable deep link, copy with on-button feedback (2.5s), optional navigator.share button, Esc/scrim/close dismiss, focus on open
- AlbumHeader + PhotoLightbox: share buttons open the sheet (album URL / photo deep link); page-level copied strips removed
- tests rewritten for sheet behavior — viewer 244 green

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

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

@@ -597,7 +597,12 @@ describe('photo lightbox interactions (UI-02 V05)', () => {
     expect(current.value).toBe('p2');
   });
 
-  it('shares via navigator.share with the album title and photo deep link; success is silent', async () => {
+  /** 分享弹层（Teleport 到 body）：从 document 定位。 */
+  function lbSheet(): HTMLElement | null {
+    return document.querySelector('.share-sheet');
+  }
+
+  it('share opens the sheet with the photo deep link; native share via sheet button', async () => {
     const share = vi.fn(() => Promise.resolve());
     Object.defineProperty(navigator, 'share', { value: share, configurable: true });
     const { wrapper } = mountV05('p1', {
@@ -608,12 +613,20 @@ describe('photo lightbox interactions (UI-02 V05)', () => {
 
     await wrapper.find('button[aria-label="分享照片"]').trigger('click');
     await flushPromises();
-    expect(share).toHaveBeenCalledWith({ title: '2026 公司年会', url: '/a/tok-lb/p/p1?lang=zh-CN' });
-    // 原生分享成功：无应用内轻提示（面板已收尾，§5.4）。
+    // 弹层出现并携带照片深链（页面级提示已退役）。
+    expect(lbSheet()).not.toBeNull();
+    expect(
+      lbSheet()!.querySelector('[data-test="share-sheet-url"]')!.textContent,
+    ).toBe('/a/tok-lb/p/p1?lang=zh-CN');
     expect(wrapper.find('.share-status').exists()).toBe(false);
+
+    const nativeBtn = lbSheet()!.querySelector<HTMLButtonElement>('[data-test="share-sheet-native"]')!;
+    nativeBtn.click();
+    await flushPromises();
+    expect(share).toHaveBeenCalledWith({ title: '2026 公司年会', url: '/a/tok-lb/p/p1?lang=zh-CN' });
   });
 
-  it('falls back to the clipboard with feedback when native share is unavailable', async () => {
+  it('sheet copy button writes the deep link with on-button feedback', async () => {
     const writeText = vi.fn(() => Promise.resolve());
     Object.defineProperty(navigator, 'clipboard', { value: { writeText }, configurable: true });
     const { wrapper } = mountV05('p1', { shareUrl: '/a/tok-lb/p/p1?lang=zh-CN' });
@@ -621,8 +634,11 @@ describe('photo lightbox interactions (UI-02 V05)', () => {
 
     await wrapper.find('button[aria-label="分享照片"]').trigger('click');
     await flushPromises();
+    const copyBtn = lbSheet()!.querySelector<HTMLButtonElement>('[data-test="share-sheet-copy"]')!;
+    copyBtn.click();
+    await flushPromises();
     expect(writeText).toHaveBeenCalledWith('/a/tok-lb/p/p1?lang=zh-CN');
-    expect(wrapper.find('.share-status').text()).toContain('链接已复制');
+    expect(copyBtn.textContent).toContain('已复制');
   });
 
   it('shows the download failure only on the photo that triggered it', async () => {