Removes the standalone `DesktopShellBootstrap` component from the desktop package, routing desktop remote mode into the shell onboarding flow instead. Updates the corresponding test file to reflect the component removal and adjusts the README.
Fusion-Task-Id: FN-3399
- Add Electron main-process IPC handlers and preload bridges for API proxying, window controls, update install, and platform lookup
- Introduce a desktop renderer entrypoint with DesktopWrapper and a custom frameless TitleBar component
- Add Electron-aware renderer utilities including API transport selection and hooks for runtime detection, auto-update events, and deep links
- Update dashboard header behavior for Electron mode and expand desktop tests across preload, transport, hooks, and title bar flows
- Document the desktop renderer architecture and update desktop package config/dependencies
