Feather MD v1.10.4

This is a critical bug fix preventing automatic, non-consensual application restarts during background update checks.

Summary:

• Safe Update Installation: Background updates are now only downloaded and prepared. The installation will never trigger automatically or force-close the application. Instead, the update is staged and waits until you click "Restart App!" to apply.

Details:

• Decoupled Update Stages: Separated retrieval and installation in src/platform/updater.js by migrating from update.downloadAndInstall() to sequential calls of update.download() and update.install().
• Specification Sync: Documented the new state transition lifecycles in PRD.md.