fix(overlay): prevent focus loss from redundant force_foreground calls

Two fixes for random focus loss on non-Win hotkeys:

1. FocusReassert handler now checks has_focus before calling
   force_foreground — skips when overlay already has keyboard focus.
   The synthetic Alt tap in force_foreground was blurring the WebView2
   input element when the overlay was already focused.

2. force_foreground returns early when GetForegroundWindow() == hwnd —
   overlay is already foreground, Alt tap + BringWindowToTop would only
   disrupt the WebView2 child's keyboard routing.