fix(desktop): align Qt app fonts with GTK (#386)

* fix(desktop): align Qt app fonts with GTK

Qt apps kept their built-in default font ("Sans Serif" 9) while GTK apps use
`gtk-font-name` (Noto Sans 11), so Telegram and other Qt apps rendered
noticeably smaller than GTK apps like Firefox. Set
QT_QPA_PLATFORMTHEME=gtk3; the plugin ships with qtbase, so it needs no
extra package and also gives Qt apps GTK file dialogs.

* chore(desktop): drop unused Xft.dpi from the Wayland GTK profile

Xft.dpi/ *.dpi are X11 X-resource settings. This file is only imported by
the niri (Wayland) hosts, where xwayland-satellite sets its own Xft.dpi
(96 x output scale, currently 144), and the i3 hosts are headless 1080p
computer-use sessions that do not import it. So the setting had no effect
anywhere; remove it instead of keeping a misleading knob.

home/linux/gui/base/desktop-tools.nix

@@ -7,6 +7,12 @@
     "MOZ_WEBRENDER" = "1";
     # enable native Wayland support for most Electron apps
     "ELECTRON_OZONE_PLATFORM_HINT" = "auto";
+    # Make Qt apps follow the GTK font and theme. Without this, Qt keeps its
+    # built-in default ("Sans Serif" 9) while GTK uses `gtk-font-name`
+    # (Noto Sans 11), so Qt apps like Telegram render visibly smaller than
+    # GTK apps. The `gtk3` platform theme plugin ships with qtbase, so no
+    # extra package is needed, and it also gets GTK file dialogs.
+    "QT_QPA_PLATFORMTHEME" = "gtk3";
     # misc
     "_JAVA_AWT_WM_NONREPARENTING" = "1";
     "QT_WAYLAND_DISABLE_WINDOWDECORATION" = "1";

home/linux/gui/base/gtk.nix

@@ -17,14 +17,6 @@
     size = 24;
   };
 
-  # set dpi for 4k monitor
-  xresources.properties = {
-    # dpi for Xorg's font
-    "Xft.dpi" = 150;
-    # or set a generic dpi
-    "*.dpi" = 150;
-  };
-
   # gtk's theme settings, generate files:
   #   1. ~/.gtkrc-2.0
   #   2. ~/.config/gtk-3.0/settings.ini