Complete v0.2.3 phrase-frequency report + register drifted sources + AGENTS.md (#10)

Clarify stable releases versus validation artifacts

Add dataset growth plot by version

Release v0.2.3 with community HPLT contribution

Add source: govpl (gov.pl government press releases) (#9)

Credit source expansion contributor

Update v0.2.1 HF card release date

Release v0.2.1 metadata schema update

Squash: collapse LFS history to reclaim private storage