Python appears in macOS Dock when Copilot CLI starts LSP servers

## Summary

When the Copilot CLI app starts a session, it launches Python LSP language servers that register as GUI applications in the macOS Dock. The Python icon appears in the Dock and persists even after the server process exits (with failure). This is disruptive — users do not expect a terminal/CLI tool to spawn visible GUI processes.

*Filed by GitHub Copilot on behalf of @hubwriter.*

## Environment

- **OS**: macOS (Darwin, Apple Silicon)
- **Copilot CLI version**: 1.0.70
- **Python**: `/usr/bin/python3` (system Python)
- **Affected LSP servers**: `lsp-python` (and possibly others — all 6 LSP servers fail on startup in this environment)

## Steps to Reproduce

1. Open the Copilot CLI app
2. Start or resume any session in a repository
3. Observe the macOS Dock

## Expected Behavior

- LSP servers should run as background-only processes
- No icons should appear in the macOS Dock or app switcher
- Failed LSP servers should not leave visible artifacts in the UI

## Actual Behavior

- Python icon appears in the macOS Dock when `lsp-python` is launched
- The icon persists even after the process exits with code 1
- This happens on every session start/refresh, repeatedly
- All 6 LSP servers (typescript, omnisharp, ruby, rust, python, go) fail to initialize but Python is the only one that shows a Dock icon

## LSP Server Status (all failing)

```
lsp-typescript — exited with code 1
lsp-omnisharp — exited with code 131
lsp-ruby — exited with code 127
lsp-rust — exited with code 1
lsp-python — exited with code 1
lsp-go — exited with code 1
```

## Suggested Fix

1. **Set `LSBackgroundOnly` or `LSUIElement`** in the Python subprocess environment or use `LSBackgroundOnly` in the process launch to prevent Dock registration
2. **Use `NSApplication.setActivationPolicy(.prohibited)`** or equivalent when spawning LSP subprocesses
3. **Do not launch LSP servers that will fail** — if the server binary is not available or crashes on startup, skip it rather than retrying each session
4. **Launch Python with `-S` or as a module** in a way that does not trigger the macOS window server registration (e.g., avoid importing Tk/tkinter)

## Workaround

Users can manually add `LSBackgroundOnly` to the Python.app Info.plist:

```bash
sudo /usr/libexec/PlistBuddy -c "Add :LSBackgroundOnly bool true" \
/Library/Frameworks/Python.framework/Versions/3.X/Resources/Python.app/Contents/Info.plist
```

But this affects all Python GUI applications system-wide, which is not ideal.

Bắt đầu bằng cách tái hiện vấn đề trên macOS, sau đó theo dõi cách Copilot CLI khởi chạy tiến trình con lsp-python và liệu các máy chủ LSP bị lỗi có được thử lại khi bắt đầu phiên hay không. So sánh môi trường khởi chạy với các tùy chọn chỉ chạy nền được đề xuất. Hoàn tất khi các máy chủ LSP chạy mà không có mục nào trong Dock hoặc trình chuyển đổi ứng dụng, và các máy chủ bị lỗi không để lại hiện vật UI cố định.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.