* fix(overlay): detect Wayland by GType so the fallback overlay stays compact (#1030)
_is_wayland() checked isinstance(display, Gdk.WaylandDisplay), but GTK3's
Gdk typelib has no WaylandDisplay class, so it always returned False. On
Wayland without gtk-layer-shell, _layout_bottom_strip() therefore sized the
prewarmed fallback window to the full monitor width (the X11 strip) instead
of the compact centered window meant for Wayland, which on KDE showed up as
a wide empty "Vocalinux Dictation" window listed in the taskbar.
Drop _is_wayland() and use _display_is_wayland(), which checks the GType
name and already gates prewarm, so both decisions agree.
Also list gtk-layer-shell as an optdepend of the source AUR package: with
it KWin and wlroots compositors get a layer surface that is never listed
in the taskbar and never needs the prewarmed toplevel. The AppImage (and
so vocalinux-bin) already bundles it.
* docs(overlay): describe the compact Wayland fallback in the overlay docstrings
The class docstring still said the overlay is always a full-width strip, which no longer holds on Wayland without layer shell (#1030).
* fix(overlay): keep the full-width strip on GNOME Wayland
Mutter ignores CENTER_ALWAYS for a plain Wayland toplevel, so the compact
fallback window landed in the top-left corner on GNOME (tested on GNOME
Shell 46 with the Ubuntu Dock). The full-width strip at least keeps the
orb horizontally centered there. Use the compact window only on KDE,
where KWin listed the strip in the taskbar as a wide empty window (#1030).
