fix(desktop): add GTK portal so file dialogs work

Home-manager's Hyprland module enables `xdg.portal` and pins the portal
search dir to the user profile with only the Hyprland backend, which has
no FileChooser implementation. File dialogs in Chromium/Electron apps
(signal, brave) fail with a DBus "No such interface
org.freedesktop.portal.FileChooser" error. Add `xdg-desktop-portal-gtk`
at the home-manager layer (system-level extraPortals aren't in the pinned
dir) and route FileChooser to it.

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

modules/home.nix

@@ -52,6 +52,12 @@ in
     # Mute the harmless "Wayland does not support QWindow::requestActivate()"
     # spam Qt apps (keepassxc) print; scoped to that one log category only.
     QT_LOGGING_RULES = "qt.qpa.wayland=false";
+    # Run Chromium/Electron apps (brave, signal, grayjay's webview) natively on
+    # Wayland instead of XWayland: nixpkgs' chromium/electron wrappers read this
+    # and inject the Ozone Wayland flags. This is a Wayland-only (Hyprland)
+    # session, so XWayland is pure downside (blurry fractional scaling, extra
+    # hop). Override per-app with --ozone-platform=x11 if one misbehaves.
+    NIXOS_OZONE_WL = "1";
     # GUI helper for ssh passphrase/PIN prompts (see sshAskpass above). Not
     # forced: with a tty ssh still prompts inline; the helper is used only when a
     # caller sets SSH_ASKPASS_REQUIRE (e.g. a headless/agent context).
@@ -282,6 +288,22 @@ in
     gtk2.configLocation = "${config.xdg.configHome}/gtk-2.0/gtkrc";
   };
 
+  # The home-manager Hyprland module below enables xdg.portal and pins the
+  # portal search dir (NIX_XDG_DESKTOP_PORTAL_DIR) to this user profile, adding
+  # only the Hyprland backend — which implements Screenshot/ScreenCast/
+  # GlobalShortcuts but not FileChooser. Add the GTK portal here (system-level
+  # extraPortals aren't in the pinned dir, so they're never seen) and route
+  # FileChooser to it, else file dialogs in Chromium/Electron apps (signal,
+  # brave) fail with a DBus "No such interface
+  # org.freedesktop.portal.FileChooser" error.
+  xdg.portal = {
+    extraPortals = [ pkgs.xdg-desktop-portal-gtk ];
+    config.common = {
+      default = [ "hyprland" "gtk" ];
+      "org.freedesktop.impl.portal.FileChooser" = [ "gtk" ];
+    };
+  };
+
   wayland.windowManager.hyprland = {
     enable = true;
     configType = "hyprlang";

modules/nixos.nix

@@ -96,7 +96,10 @@
   # so the Secret Service is open without a second passphrase.
   security.pam.services.greetd.enableGnomeKeyring = true;
 
-  # XDG portals (screen sharing, file pickers, and so on).
+  # XDG portals (screen sharing, file pickers, and so on). The GTK portal (for
+  # file dialogs) is added at the home-manager layer, not here: home-manager's
+  # Hyprland module pins the portal search dir to the user profile, so a portal
+  # listed in this system-level extraPortals is never seen. See modules/home.nix.
   xdg.portal = {
     enable = true;
     extraPortals = [ pkgs.xdg-desktop-portal-hyprland ];