fix(file-viewer): phones ignore expand and the grip, folder paging follows history, swallow Alt+arrows

Under 600px the window stays full screen whatever Expand or a drag says, and both
controls are hidden. Stepping onto a folder-grid entry goes through the grid so its
index follows. Alt+left/right is swallowed at the ends of the list too. Adds tests
for the key handler, the grip clamp and the history/grid case, zh-CN titles and wiki lines.

src/web/public/i18n.js

@@ -1039,6 +1039,13 @@
     'Source type filter': '来源类型筛选',
     'Copy content': '复制内容',
     'Edit file': '编辑文件',
+    'Back (Alt+←)': '后退 (Alt+←)',
+    'Forward (Alt+→)': '前进 (Alt+→)',
+    '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',
     'Wrap lines': '自动换行',

src/web/public/mobile.css

@@ -2298,6 +2298,19 @@ html.mobile-init .file-browser-panel {
     border-right: none;
   }
 
+  /* Expand and the resize grip would only shrink the full-screen window (96vw x 94vh,
+     or a px size left by a drag in landscape), so a phone ignores both. */
+  .file-preview-window,
+  .file-preview-window.expanded {
+    width: 100vw !important;
+    height: var(--app-height, 100vh) !important;
+  }
+
+  #filePreviewExpandBtn,
+  .file-preview-resize {
+    display: none;
+  }
+
   .file-preview-editbar {
     padding-bottom: calc(0.4rem + var(--safe-area-bottom));
   }

src/web/public/panels-ui.js

@@ -4583,6 +4583,13 @@ Object.assign(CodemanApp.prototype, {
     // only needs to cover the call itself.
     this._filePreviewHistoryStepping = true;
     try {
+      // A folder-grid page goes through the grid so index, lastIndex and the highlighted
+      // tile follow; otherwise the next ‹ › would continue from the newer file.
+      const folderFile = e.options?.folderFile;
+      if (folderFile && folderFile.folderId === this.folderGrid?.folderId) {
+        const index = this.folderGrid.files.findIndex((f) => f.name === folderFile.name);
+        if (index !== -1) return this._openFolderGridFile(index);
+      }
       return this.openFilePreview(e.filePath, e.sessionId, e.attachmentId, e.options || {});
     } finally {
       this._filePreviewHistoryStepping = false;
@@ -4639,11 +4646,13 @@ Object.assign(CodemanApp.prototype, {
         if (!this.$('filePreviewOverlay')?.classList.contains('visible')) return;
         const t = ev.target;
         if (t && (t.isContentEditable || (/^(INPUT|TEXTAREA|SELECT)$/.test(t.tagName) && !t.classList?.contains('xterm-helper-textarea')))) return;
+        // Swallowed even at the ends of the list: otherwise the terminal behind the overlay
+        // types it as word-left/right, and on a header button the browser's own Alt+← goes Back.
+        ev.preventDefault();
+        ev.stopPropagation();
         const h = this.filePreviewHistory;
         const delta = ev.key === 'ArrowLeft' ? -1 : 1;
         if (!h || h.index + delta < 0 || h.index + delta >= h.entries.length) return;
-        ev.preventDefault();
-        ev.stopPropagation();
         this.stepFilePreviewHistory(delta);
       },
       true