feat(data): european_hplt_v3_pl expansion WDS bins 10-5 (+1.49M docs / 2.04B tok)

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

Merge main into PR 8 and preserve NKJP source

Add source: european_hplt_v3_pl (HPLT v3.0 Polish, top WDS bins, CC0) (#5)

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

Add source: nkjp1m

Release v0.3.1 Europeana preview shard (#4)

Update v0.2.1 HF card release date

Release v0.2.1 metadata schema update

Squash: collapse LFS history to reclaim private storage