File preview panel: copy-to-clipboard icon no longer appears

**Description**
In the Claude Code desktop app's file preview panel (the side panel that shows a selected file's contents, e.g. a .txt report), there used to be a copy-to-clipboard icon in the panel header. It no longer appears.

**Environment**
- Claude Code version: 2.1.250
- Platform: Windows 11 Pro (win32)
- Client: Desktop app (Code tab)

**Expected behavior**
A copy icon in the file preview panel header to copy the file's contents to clipboard.

**Actual behavior**
The icon is missing; only search/more-options/expand/close icons remain in the panel header.

**Additional context**
Not sure exactly when this was removed — noticed it recently while viewing a .txt report file in the panel.

Start by reproducing the issue in the Claude Code desktop app on Windows 11 and inspect the file preview panel header for the missing control. Compare the current header with the described expected behavior; done means the copy-to-clipboard icon is visible and copies the selected file's contents.

Written by the indexing model from the issue text.