No option to use native/system window title bar on Linux

[nigussolomon]

On Linux, t3-code draws its own custom title bar (frame: false) instead of
using the desktop environment's native window decorations. This causes it to look
visually inconsistent with other apps on themed setups — for example, on KDE Plasma
with a macOS-style theme (traffic-light buttons), t3-code shows its own
Windows-style minimize/maximize/close icons instead of matching.

A setting (or a documented launch flag) to enable the native/system title bar on
Linux, similar to VS Code's "window.titleBarStyle": "native" option. This would let
users match their desktop theme instead of being stuck with the app's built-in
custom chrome.