feat(electron): add persistent UI scale setting

apps/desktop/preload/apis/core.ts

@@ -123,5 +123,9 @@ export const extendedApi = {
     setDesktopCloseBehavior: (behavior: DesktopCloseBehavior): Promise<{ success: boolean; error?: string }> => {
       return ipcRenderer.invoke('app:setDesktopCloseBehavior', behavior)
     },
+    getDesktopUiScale: (): Promise<number> => ipcRenderer.invoke('app:getDesktopUiScale'),
+    setDesktopUiScale: (scale: number): Promise<{ success: boolean; error?: string }> => {
+      return ipcRenderer.invoke('app:setDesktopUiScale', scale)
+    },
   },
 }

apps/desktop/preload/index.d.ts

@@ -194,6 +194,8 @@ interface Api {
     setOpenAtLogin: (enabled: boolean) => Promise<{ success: boolean; error?: string }>
     getDesktopCloseBehavior: () => Promise<DesktopCloseBehavior>
     setDesktopCloseBehavior: (behavior: DesktopCloseBehavior) => Promise<{ success: boolean; error?: string }>
+    getDesktopUiScale: () => Promise<number>
+    setDesktopUiScale: (scale: number) => Promise<{ success: boolean; error?: string }>
   }
 }