window-management: toggle for macOS-style window controls position

Adds a new toggler "Place buttons on the left (macOS style)" in
*Desktop → Window Management → Window controls*, next to the existing
show_maximize / show_minimize controls. When enabled, writes
`WindowControlsPosition::Start` into the `CosmicTk` config
(com.system76.CosmicTk); when disabled, writes `End` (default).

All libcosmic-based applications rebuilt against a libcosmic that
exposes `WindowControlsPosition` pick up the change live through the
existing cosmic-config subscription.

Includes:
- new Message variant WindowControlsPositionStart(bool) + handler
- `window-controls.position-start` fluent key added in en + fr locales
- Cargo.toml: activate local [patch] override to libcosmic (dev only,
  not suitable for upstream merge)

Requires: libcosmic >= 5c331935 (header_bar WindowControlsPosition).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.toml

@@ -70,12 +70,12 @@ cosmic-client-toolkit = { git = "https://github.com/pop-os/cosmic-protocols//",
 # cosmic-settings-config = { git = "https://github.com/pop-os/cosmic-settings-daemon//", branch = "input_nobuild" }
 
 # For development and testing purposes
-# [patch.'https://github.com/pop-os/libcosmic']
-# libcosmic = { path = "../libcosmic" }
-# cosmic-config = { path = "../libcosmic/cosmic-config" }
-# cosmic-theme = { path = "../libcosmic/cosmic-theme" }
-# iced_futures = { path = "../libcosmic/iced/futures" }
-# iced_winit = { path = "../libcosmic/iced/winit" }
+[patch.'https://github.com/pop-os/libcosmic']
+libcosmic = { path = "../libcosmic" }
+cosmic-config = { path = "../libcosmic/cosmic-config" }
+cosmic-theme = { path = "../libcosmic/cosmic-theme" }
+iced_futures = { path = "../libcosmic/iced/futures" }
+iced_winit = { path = "../libcosmic/iced/winit" }
 
 # libcosmic = { git = "https://github.com/pop-os/libcosmic//" }
 # cosmic-config = { git = "https://github.com/pop-os/libcosmic//" }

cosmic-settings/src/pages/desktop/window_management.rs

@@ -27,6 +27,7 @@ pub enum Message {
     ShowActiveWindowHint(bool),
     ShowMaximizeButton(bool),
     ShowMinimizeButton(bool),
+    WindowControlsPositionStart(bool),
     SetEdgeSnapThreshold(u32),
     Surface(surface::Action),
 }
@@ -177,6 +178,19 @@ impl Page {
                         .set_show_minimize(&config, value);
                 }
             }
+            Message::WindowControlsPositionStart(left) => {
+                if let Ok(config) = cosmic::config::CosmicTk::config() {
+                    let position = if left {
+                        cosmic::widget::WindowControlsPosition::Start
+                    } else {
+                        cosmic::widget::WindowControlsPosition::End
+                    };
+                    let _res = cosmic::config::COSMIC_TK
+                        .write()
+                        .unwrap()
+                        .set_window_controls_position(&config, position);
+                }
+            }
             Message::ShowActiveWindowHint(value) => {
                 self.show_active_hint = value;
                 if let Err(err) = self.comp_config.set("active_hint", value) {
@@ -274,6 +288,7 @@ pub fn window_controls() -> Section<crate::pages::Message> {
         maximize = fl!("window-controls", "maximize");
         minimize = fl!("window-controls", "minimize");
         active_window_hint = fl!("window-controls", "active-window-hint");
+        position_start = fl!("window-controls", "position-start");
     });
 
     Section::default()
@@ -296,6 +311,13 @@ pub fn window_controls() -> Section<crate::pages::Message> {
                     settings::item::builder(&descriptions[minimize])
                         .toggler(cosmic::config::show_minimize(), Message::ShowMinimizeButton),
                 )
+                .add(settings::item::builder(&descriptions[position_start]).toggler(
+                    matches!(
+                        cosmic::config::window_controls_position(),
+                        cosmic::widget::WindowControlsPosition::Start
+                    ),
+                    Message::WindowControlsPositionStart,
+                ))
                 .apply(Element::from)
                 .map(crate::pages::Message::WindowManagement)
         })

i18n/en/cosmic_settings.ftl

@@ -484,6 +484,7 @@ window-controls = Window controls
     .maximize = Show maximize button
     .minimize = Show minimize button
     .active-window-hint = Show active window hint
+    .position-start = Place buttons on the left (macOS style)
 
 focus-navigation = Focus navigation
     .focus-follows-cursor = Focus follows cursor

i18n/fr/cosmic_settings.ftl

@@ -322,6 +322,7 @@ window-controls = Contrôles des fenêtres
     .maximize = Afficher le bouton maximiser
     .minimize = Afficher le bouton minimiser
     .active-window-hint = Afficher l'indice de la fenêtre active
+    .position-start = Placer les boutons à gauche (style macOS)
 focus-navigation = Navigation par le focus
     .focus-follows-cursor = Le focus suit le curseur
     .focus-follows-cursor-delay = Délai de suivi du focus en ms