Save and restore window position and size

Problem

Native Rake windows open at their default size and position on every launch. Users expect a desktop app to reopen where they left it. Today each app would have to build that itself.

Proposal

An opt-in policy on App, stored through the existing preferences service:

• On move, resize, fullscreen change and close, save each window's bounds, display, and maximized or fullscreen state under a stable window key.
• On launch, restore it. If the saved display is gone, or the bounds are now off-screen, fall back to the default placement.
• Write at most once per short interval while the user is dragging or resizing.
• Let apps opt out per window and reset the saved state.

gpui-pre has window_bounds() and restore_native_window_state(), so most of this is wiring.

Out of scope

• Web, where the browser owns the window.
• Restoring tabs and routes. Durable session restore is a separate topic.

Done when

• The desktop example reopens at its saved size and position on macOS, Windows and Linux (X11 and Wayland). Results include each OS version and display setup tested.
• Tests cover off-screen bounds, a disconnected display, mixed display scales and corrupt saved data.
• Wayland limits are documented, because compositors may not let apps place windows.

Depends on

The move from GPUI CE to gpui-pre.