Add 0.9.1 release notes

[austin-smith]

What Changed

Add the 0.9.1 changelog entry with per-item PR references and the v0.9.0...v0.9.1 comparison link.

Why

Document the user-visible changes since v0.9.0 in preparation for the next patch release.

Validation

• Reviewed all six merged PRs since v0.9.0 against the release baseline and final code.
• Reviewed the complete diff and verified PR references and version tags.
• git diff --check passed.
• Autoreview and its secret scan passed before the final wording simplification; the simplified wording was reviewed directly.
• Documentation-only change; no builds or tests required.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-06T17:12:44.624879Z	25236be	PR opened

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