changelog: refresh reference-link definitions for 0.3.0

Address the Copilot review: point [Unreleased] at v0.3.0...HEAD, add the
[0.3.0] compare link, and backfill the [0.2.0] link the previous release
left out — so every bracketed version heading resolves.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: MarkusNeusinger

CHANGELOG.md

@@ -145,5 +145,7 @@ First public, pip-installable release (`pip install cite-citadel`), and the PyPI
 - Shared citation/link/fence parsing consolidated into `grammar.py`; viewer moved to a subpackage
   with a golden bundle test; Office/OLE extraction isolated.
 
-[Unreleased]: https://github.com/MarkusNeusinger/cite-citadel/compare/v0.1.0...HEAD
+[Unreleased]: https://github.com/MarkusNeusinger/cite-citadel/compare/v0.3.0...HEAD
+[0.3.0]: https://github.com/MarkusNeusinger/cite-citadel/compare/v0.2.0...v0.3.0
+[0.2.0]: https://github.com/MarkusNeusinger/cite-citadel/compare/v0.1.0...v0.2.0
 [0.1.0]: https://github.com/MarkusNeusinger/cite-citadel/releases/tag/v0.1.0