Merges five features: **Launch mode persistence** (FN-3405) — desktop now remembers and restores the user's preferred window mode across restarts via an IPC bridge; **Mailbox detail pane** (FN-3719/3720) — clicking messages in the Mail tab and Mailbox opens the detail pane and reply panel; **Remote
Fusion-Task-Id: FN-3405
- Add electron-updater dependency and implement native desktop integration utilities for dialogs, notifications, auto-update wiring, and window state persistence
- Add fusion:// deep-link protocol registration, URL parsing, single-instance handlers, and renderer event forwarding for task/project routes
- Add comprehensive Vitest coverage for native integrations and deep-link handling across success, edge, and failure cases
- Document native and deep-link API contracts, behavior, and usage details in the desktop package README
