feat: add desktop UI password setting

Adds optional desktop UI password protection
Starts Electron with the saved UI password
Explains login session duration in settings

packages/ui/src/lib/desktop.ts

@@ -52,6 +52,7 @@ export type DesktopSettings = {
   // Optional absolute path to `opencode` binary.
   opencodeBinary?: string;
   desktopLanAccessEnabled?: boolean;
+  desktopUiPassword?: string;
   projects?: ProjectEntry[];
   activeProjectId?: string;
   approvedDirectories?: string[];