chore: cut the v1.9.0 changelog

[jferrl]

Description

Turns [Unreleased] into [v1.9.0] - 2026-09-19 and adds the one-line summary the
other version sections carry.

The summary says the library is unchanged. A minor bump on an auth package invites a
careful reader to hunt for behaviour changes, and there are none here: this release is the
CLI and its distribution.

Merge this, then tag:

git checkout main && git pull
git tag v1.9.0 && git push origin v1.9.0

Type of Change

• 📚 Documentation update

Testing

Not applicable — no code changes.

Documentation

• I have updated the CHANGELOG.md file

Checklist

• I have performed a self-review of my own code
• I have checked my code and corrected any misspellings

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.96%. Comparing base (2d94e7b) to head (1d4a894).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #73   +/-   ##
=======================================
  Coverage   96.96%   96.96%           
=======================================
  Files           5        5           
  Lines         462      462           
=======================================
  Hits          448      448           
  Misses         14       14           

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