PerKeyEditor: rebuild tool icons on GTK theme change

Tool icon pixbufs are baked at construction time using the button's
current style context foreground color. Without this, switching the
desktop theme (e.g. light <-> dark) at runtime leaves the editor's
icons stuck in the previous color while the rest of the UI updates.

Subscribe to Gtk.Settings notify::gtk-theme-name and
notify::gtk-application-prefer-dark-theme; on either, replace each
themed button's child Gtk.Image with a freshly-recolored one.
Disconnect both signals from PerKeyEditor.shutdown so the editor
doesn't leak handlers across openings.

lib/solaar/ui/perkey/editor.py

@@ -130,6 +130,9 @@ class PerKeyEditor(Gtk.Box):
         # toolbar row
         toolbar = Gtk.Box(orientation=Gtk.Orientation.HORIZONTAL, spacing=8)
         self._tool_buttons: dict[str, Gtk.RadioButton] = {}
+        # Track which buttons display a themed icon, so we can re-render them
+        # when the active GTK theme switches (light <-> dark, theme name).
+        self._themed_icon_buttons: dict[Gtk.RadioButton, str] = {}
         self._gradient_swatch: GradientSwatch | None = None
         first: Gtk.RadioButton | None = None
         supported = layout.supported_tools if layout else ("single", "rect", "bucket", "gradient")
@@ -150,6 +153,7 @@ class PerKeyEditor(Gtk.Box):
                     btn.add(image)
                     btn.set_tooltip_text(tip or label)
                     btn.get_accessible().set_name(label)
+                    self._themed_icon_buttons[btn] = icon_name
                 else:
                     btn.set_label(label)
                     btn.set_tooltip_text(tip)
@@ -159,6 +163,14 @@ class PerKeyEditor(Gtk.Box):
             toolbar.pack_start(btn, False, False, 0)
             self._tool_buttons[name] = btn
 
+        # Re-render themed icons when the GTK theme changes at runtime.
+        self._theme_signal_handlers: list[tuple[object, int]] = []
+        if self._themed_icon_buttons:
+            settings = Gtk.Settings.get_default()
+            for prop in ("notify::gtk-theme-name", "notify::gtk-application-prefer-dark-theme"):
+                hid = settings.connect(prop, self._on_gtk_theme_changed)
+                self._theme_signal_handlers.append((settings, hid))
+
         initial_active, initial_previous = 0xFF0000, 0xFF0000
         try:
             persisted = sink.palette_state()
@@ -209,6 +221,24 @@ class PerKeyEditor(Gtk.Box):
             except Exception as e:
                 logger.debug("perkey sink unsubscribe failed: %s", e)
             self._unsubscribe = None
+        for obj, hid in self._theme_signal_handlers:
+            try:
+                obj.disconnect(hid)
+            except Exception as e:
+                logger.debug("theme signal disconnect failed: %s", e)
+        self._theme_signal_handlers = []
+
+    def _on_gtk_theme_changed(self, _settings, _pspec) -> None:
+        """Rebuild themed tool icons so they match the new theme's foreground."""
+        for btn, icon_name in self._themed_icon_buttons.items():
+            old = btn.get_child()
+            new_image = _tool_icon_image(icon_name, btn)
+            if new_image is None:
+                continue
+            if old is not None:
+                btn.remove(old)
+            btn.add(new_image)
+            new_image.show()
 
     def canvas_size(self) -> tuple[int, int]:
         """Return the canvas's pixel size_request — what the dialog should