docs(changelog): 0.9.0 release notes

[gtrrz-victor]

Changelog entry for the 0.9.0 release, covering ~90 PRs merged since v0.8.42.

Highlights

• git-refs checkpoint backend becomes the default; adds entire doctor migrate-checkpoints, second-device discovery, and checkpoint list --json
• entire search routes to the v4 query-serve path with cross-cell fan-out; v3 removed (feat(search)!: route entire search to the v4 query-serve path (cross-cell fan-out, v3 removed) #1800)
• Broad fixes across enable/setup, checkpoint push, hooks latency, Windows, explain, redaction, and attribution

Thanks

External contributor @MuskanPaliwal (#1359, #1186).

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds the release notes section for v0.9.0 to the project changelog, summarizing the most user-visible CLI features, fixes, and housekeeping since v0.8.42, including an explicit breaking-change callout.

Changes:

• Add a new 0.9.0 section dated 2026-07-27 with Added / Changed / Fixed / Housekeeping / Thanks groupings.
• Document notable highlights like git-refs becoming the default checkpoint backend and cross-cell entire search routing (breaking).
• Credit an external contributor in a dedicated “Thanks” section.

Comments suppressed due to low confidence (1)

CHANGELOG.md:29

• Consider adding an explicit “Changed” bullet for switching the default checkpoint backend to git-refs, rather than embedding it in the “Added” section. That makes the behavior change more discoverable alongside the other user-facing changes.

- **Breaking:** `entire search` now routes to the v4 query-serve path with cross-cell fan-out; the v3 path is removed ([#1800](https://github.com/entireio/cli/pull/1800))