docs(file-viewer): list Alt+Left/Right in the shortcut overlay and help

Merge-time fix for #659.

- Alt+Left/Right (File Viewer back/forward) is a display-only entry in
  DEFAULT_SHORTCUTS, so the Ctrl+? overlay lists it, and a row in the
  help modal's Panels group, pinned in help-modal-shortcuts.test.ts.
  zh-CN entry for the new label; the "Restore size" entry is dropped,
  since nothing shows that string any more.
- The wiki row moves from "Sessions and tabs" to "Everything else".
- The grip comment in styles.css says only phones hide the grip;
  tablets show and use it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/public/app.js

@@ -685,6 +685,14 @@ const DEFAULT_SHORTCUTS = [
     label: 'Close Panels',
     displayBindings: ['Escape'],
   },
+  // Handled by the File Viewer's own capture-phase listener while it is open
+  // (_bindFilePreviewChrome, panels-ui.js), never through the registry.
+  {
+    id: 'file-preview-history',
+    group: 'Panels',
+    label: 'File Viewer Back / Forward',
+    displayBindings: ['Alt/Option+ArrowLeft', 'Alt/Option+ArrowRight'],
+  },
 ];
 
 

src/web/public/i18n.js

@@ -1044,7 +1044,6 @@
     'Back to the previous file': '返回上一个文件',
     'Forward to the next file': '前进到下一个文件',
     Expand: '展开',
-    'Restore size': '恢复大小',
     'Drag to resize': '拖动以调整大小',
     'Rendered markdown': '渲染 Markdown',
     'Line numbers': '行号',
@@ -1242,6 +1241,7 @@
     'Voice input (Ctrl+Shift+V)': '语音输入（Ctrl+Shift+V）',
     'Insert Newline': '插入换行',
     'Close Panels': '关闭面板',
+    'File Viewer Back / Forward': '文件查看器后退 / 前进',
     'Previous / Next Session': '上一个 / 下一个会话',
     'Next Session': '下一个会话',
     'Previous Session': '上一个会话',

src/web/public/index.html

@@ -926,6 +926,7 @@
               <div><kbd>Ctrl</kbd>+<kbd>?</kbd></div><div>Show Shortcuts</div>
               <div><kbd>Alt/Option</kbd>+<kbd>?</kbd></div><div>Show Shortcuts</div>
               <div><kbd>Escape</kbd></div><div>Close Panels</div>
+              <div><kbd>Alt/Option</kbd>+<kbd>ArrowLeft</kbd> / <kbd>Alt/Option</kbd>+<kbd>ArrowRight</kbd></div><div>File Viewer Back / Forward</div>
             </div>
           </section>
         </div>

src/web/public/styles.css

@@ -12251,7 +12251,8 @@ html:is([data-skin="paper-gray"], [data-skin="solarized-light"], [data-skin="cat
 
 /* Corner grip (panels-ui.js _bindFilePreviewResize). The window is centred, so a
    drag moves both edges: the handler doubles the pointer delta to keep the corner
-   under the pointer. Touch devices use the Expand button instead. */
+   under the pointer. Only phones hide it (with Expand, mobile.css under 600px), since
+   the window is full screen there; tablets show and use it. */
 .file-preview-resize {
   position: absolute;
   right: 0;