host: a restored window fits the monitor it opens on

A state saved on a larger or rearranged screen (2720x1800 at x=3347 on a smaller second monitor)
left the titlebar off-screen and the window could not be moved. After the window-state restore,
the window is moved inside, and shrunk to, the work area of the monitor it is mostly on (the
primary one when that monitor is gone). Maximized and full-screen windows are left to the OS.
window_fit::fit is pure and unit tested.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/waybetter-host/src/lib.rs

@@ -76,6 +76,7 @@ pub mod tabs;
 pub mod testkit;
 pub mod theme;
 pub mod update;
+pub mod window_fit;
 pub mod workspaces;
 pub mod zoom;