qt: pass negative KDE settings as values

Insert the command-option terminator before values passed to kwriteconfig6 so negative numeric settings are not parsed as command flags.

This fixes KDE settings such as DimDisplayIdleTimeoutSec = -1, which previously produced an unknown-option error from kwriteconfig6.

Cover the regression in the existing qt-basic NMT test by checking the generated activation command includes the terminator before the negative value.

modules/misc/qt/kconfig.nix

@@ -65,9 +65,9 @@ in
             if v == null then
               "--delete"
             else if t == "bool" then
-              "--type bool ${builtins.toJSON v}"
+              "--type bool -- ${builtins.toJSON v}"
             else
-              lib.escapeShellArg (toString v);
+              "-- ${lib.escapeShellArg (toString v)}";
           toLine =
             file: path: value:
             if builtins.isAttrs value then

tests/modules/misc/qt/qt-basic.nix

@@ -1,10 +1,14 @@
 {
   qt.enable = true;
 
+  qt.kde.settings.powerdevilrc.AC.Display.DimDisplayIdleTimeoutSec = -1;
+
   nmt.script = ''
     assertFileRegex home-path/etc/profile.d/hm-session-vars.sh \
       'QT_PLUGIN_PATH'
     assertFileRegex home-path/etc/profile.d/hm-session-vars.sh \
       'QML2_IMPORT_PATH'
+    assertFileRegex activate \
+      "kwriteconfig6 .*--file '/home/hm-user/.config/powerdevilrc' .*--key DimDisplayIdleTimeoutSec -- -1"
   '';
 }