feat(hyprlua): float xdg portal dialogs above their parent

Portal-backed file/app choosers (xdg-desktop-portal-gtk) — e.g. Steam's
"select library folder" picker, plus Chromium/Electron/Flatpak dialogs —
run in a separate process and open as parentless top-levels with no
xdg-dialog or X11-dialog hint. Hyprland can't tell they're dialogs and
tiles them, unlike in-process xdg dialogs which it auto-floats. Match the
portal backend's class and float + centre it so it lands above its parent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

desktopenvs/hyprlua/hypr/usr/windowrules.lua

@@ -89,6 +89,21 @@ hl.window_rule({
     move  = "(cursor_x-380) (cursor_y-230)",
 })
 
+-- xdg portal dialogs — float, centred on the monitor (i.e. above the parent).
+-- The GTK portal backend (xdg-desktop-portal-gtk) serves native file/app/print
+-- choosers for portal-driven apps: Steam ("select library folder"), Chromium/
+-- Electron, Flatpak apps, etc. It runs in its *own* process, so the dialog opens
+-- as a parentless top-level with no xdg-dialog/X11-dialog hint — Hyprland has no
+-- signal that it's a dialog and would otherwise tile it (unlike in-process xdg
+-- dialogs, which it auto-floats). Natural size is kept, so the centre offsets use
+-- the real window_w/window_h (no `size` to skew them; see the filepicker note).
+hl.window_rule({
+    name  = "xdg-portal-dialog",
+    match = { class = "xdg-desktop-portal-gtk" },
+    float = true,
+    move  = "(monitor_w/2 - window_w/2) (monitor_h/2 - window_h/2)",
+})
+
 -- spotify floating
 hl.window_rule({
     name    = "spotify-float",