qt: again disable changing light/dark theme at runtime

partially reverts 11a04c0d72

related https://github.com/spesmilo/electrum/issues/7209

electrum/gui/qt/__init__.py

@@ -147,6 +147,15 @@ class ElectrumGui(BaseElectrumGui, Logger):
         self.tray.show()
 
     def reload_app_stylesheet(self):
+        """Set the Qt stylesheet and custom colors according to the user-selected
+        light/dark theme.
+        TODO this can ~almost be used to change the theme at runtime (without app restart),
+             except for util.ColorScheme... widgets already created with colors set using
+             ColorSchemeItem.as_stylesheet() and similar will not get recolored.
+             See e.g.
+             - in Coins tab, the color for "frozen" UTXOs, or
+             - in TxDialog, the receiving/change address colors
+        """
         use_dark_theme = self.config.get('qt_gui_color_theme', 'default') == 'dark'
         if use_dark_theme:
             try:

electrum/gui/qt/settings_dialog.py

@@ -259,7 +259,8 @@ class SettingsDialog(WindowModalDialog):
         colortheme_label = QLabel(_('Color theme') + ':')
         def on_colortheme(x):
             self.config.set_key('qt_gui_color_theme', colortheme_combo.itemData(x), True)
-            self.window.gui_object.reload_app_stylesheet()
+            #self.window.gui_object.reload_app_stylesheet()
+            self.need_restart = True
         colortheme_combo.currentIndexChanged.connect(on_colortheme)
         gui_widgets.append((colortheme_label, colortheme_combo))