chore(release): cut v0.8.3

[danielewood]

Summary

• cut the 0.8.3 changelog release section dated 2026-03-09
• reset Unreleased and advance the compare links
• add the missing [#132] changelog link definition

Testing

• pre-commit run --all-files
• pre-commit run --files CHANGELOG.md

[Copilot]

Pull request overview

Updates the project changelog for the 0.8.3 release, adding a new version section and adjusting link references consistent with Keep a Changelog/SemVer formatting.

Changes:

• Add a ## [0.8.3] - 2026-03-09 release section immediately after ## [Unreleased].
• Update the [Unreleased] compare link to start from v0.8.3 and add a [0.8.3] compare link.
• Add a link reference for PR [#132].

[Copilot]

[#130] is referenced in the 0.8.3 change list, but there is no corresponding link reference definition ([#130]: ...) in the link section at the bottom. Add the missing reference (or remove/convert the reference) so the Markdown renders with a working link.

Suggested change

	[#129]: https://github.com/sensiblebit/certkit/pull/129
	[#129]: https://github.com/sensiblebit/certkit/pull/129
	[#130]: https://github.com/sensiblebit/certkit/pull/130