Window position and size reset once on upgrade

What changed

The main window and the Quick Assistant window now remember their position and size through WindowManager's built-in bounds persistence (backed by the main-process persist cache) instead of the electron-window-state library. The old per-window state files (window-state.json, quickAssistant-state.json) are no longer read.

Why this matters to the user

On the first launch after upgrading, both windows open at their default position and size once. From then on, position/size (and the main window's maximized state) are remembered across restarts as before, including restoring onto the display the window was last on.

What the user should do

Nothing — this is automatic. The one-time reset is expected; the old state files are simply left behind (not migrated, not deleted) because window geometry is non-critical and regenerable.

Notes for release manager

Pairs with the removal of the electron-window-state dependency and the new rememberBounds WindowManager capability. Only Main + QuickAssistant are affected this round.