Release 0.9.0

[Vasanthdev2004]

Summary

Prepare v0.9.0 for the save-health dashboard and restart-safe backup/upload recovery merged in #67.

• Bump package metadata and the CLI version together from 0.8.4 to 0.9.0.
• Finalize the changelog, including the dashboard shutdown-race fix.
• Document watcher restart requirements, automatic migration, and retention of pending snapshots.

Release gates

• Version fields agree at 0.9.0; runtime dependency declaration check passes.
• Run full CI and the manually dispatched Windows installer check on this candidate before merging/tagging.
• Publish only after those checks pass. The tag-triggered release workflow builds and attaches the portable executable and Windows installer.

No product behavior, dependencies, installer settings, user saves, or cloud settings are changed by this release-preparation PR.