[Bug] Cannot copy Copilot CLI output to clipboard in VSCode Server (browser-based remote environment)

# [Bug] Cannot copy Copilot CLI output to clipboard in VSCode Server (browser-based remote environment)

## Summary

When using GitHub Copilot CLI inside a **VSCode Server** environment (web-based, accessed via browser), the "copy to clipboard" functionality silently fails. There is no fallback, no error message, and no way to retrieve the output that was supposed to be copied.

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## Environment

| Item | Value |
|---|---|
| OS | Ubuntu 22.04.4 LTS |
| VSCode Server | Web-based (`--host 0.0.0.0 --port 8080`, no GUI) |
| Terminal | tmux inside VSCode Server integrated terminal |
| `$DISPLAY` | *(empty — no X11 server)* |
| `$WAYLAND_DISPLAY` | *(empty — no Wayland compositor)* |
| `xclip` | not found |
| `xsel` | not found |
| `wl-copy` | not found |
| `pbcopy` | not found (Linux) |
| TTY | `not a tty` |
| Copilot CLI version | 1.0.67 |

Relevant environment variables confirming VSCode Server context:
```
VSCODE_IPC_HOOK_CLI=/tmp/vscode-ipc-*.sock
TERM_PROGRAM=tmux
BROWSER=/usr/lib/vscode-server/bin/helpers/browser.sh
ENTRYPOINT=vscode-server --host 0.0.0.0 --port 8080 --without-connection-token
```

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## Steps to Reproduce

1. Connect to a remote machine running **VSCode Server** via browser (e.g., `http://:8080`).
2. Open an integrated terminal (which runs inside a tmux/screen session without a display server).
3. Use GitHub Copilot CLI and trigger any action that copies output to clipboard (e.g., accepting a suggested command).
4. Attempt to paste anywhere — clipboard is empty.

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## Expected Behavior

One of the following should happen:

**make copy avaliable**

In the same env, codex does;

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## Actual Behavior

The clipboard copy action **silently fails**. No output is printed, no warning is shown. The user has no way to access the content that was supposed to be copied.

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Beginne damit, den Fehler beim Kopieren in der dokumentierten Umgebung mit VSCode Server, integrated-terminal und tmux zu reproduzieren. Verfolge anschließend die Kopieraktion der CLI und deren Verhalten, wenn keine Anzeige oder kein Dienstprogramm für die Zwischenablage verfügbar ist. Als erledigt gilt die Aufgabe, wenn die Ausgabe kopierbar ist oder ein klarer Fallback bzw. Fehler sie abrufbar macht, statt dass sie lautlos fehlschlägt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.