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.

Empieza reproduciendo el problema en macOS y, a continuación, rastrea cómo Copilot CLI inicia el subproceso lsp-python y si los servidores LSP fallidos se reintentan al iniciar la sesión. Compara el entorno de lanzamiento con las opciones sugeridas de ejecución exclusiva en segundo plano. Se considera terminado cuando los servidores LSP se ejecutan sin entradas en el Dock ni en el selector de aplicaciones, y los servidores fallidos no dejan artefactos persistentes en la UI.

Escrito por el modelo de indexación a partir del texto del issue.