feat(commands-v2): add v2 titlebar-mode commands, drop v2_set_use_system_titlebar

The new commands cover get, set, and platform availability. The legacy
boolean setter is removed because the mode enum is now authoritative.

cc

src-tauri/src/commands_v2/settings.rs

@@ -9,6 +9,7 @@ use crate::config::playback_preferences::{
 use crate::config::tray_settings::TraySettings;
 use crate::config::tray_settings::TraySettingsState;
 use crate::config::window_settings::WindowSettingsState;
+use crate::config::window_settings::{available_titlebar_modes, is_sandboxed, TitlebarMode};
 use crate::core_bridge::CoreBridgeState;
 use crate::AppState;
 
@@ -22,11 +23,32 @@ pub async fn v2_set_api_locale(locale: String, state: State<'_, AppState>) -> Re
 }
 
 #[tauri::command]
-pub fn v2_set_use_system_titlebar(
-    value: bool,
+pub fn v2_get_titlebar_mode(
+    state: State<'_, WindowSettingsState>,
+) -> Result<TitlebarMode, String> {
+    state.get_titlebar_mode()
+}
+
+#[tauri::command]
+pub fn v2_set_titlebar_mode(
+    mode: TitlebarMode,
     state: State<'_, WindowSettingsState>,
 ) -> Result<(), String> {
-    state.set_use_system_titlebar(value)
+    state.set_titlebar_mode(mode)
+}
+
+#[derive(serde::Serialize)]
+pub struct TitlebarModeAvailability {
+    pub modes: Vec<TitlebarMode>,
+    pub sandboxed: bool,
+}
+
+#[tauri::command]
+pub fn v2_available_titlebar_modes() -> TitlebarModeAvailability {
+    TitlebarModeAvailability {
+        modes: available_titlebar_modes(),
+        sandboxed: is_sandboxed(),
+    }
 }
 
 #[tauri::command]