Proofpress v0.3.0

What's Changed

• Fix GitHub Release creation in npm workflow by @chenmingtang830 in #11
• Add repository social preview image by @chenmingtang830 in #12
• Add Artifact Provenance Protocol core by @chenmingtang830 in #13
• docs: frame Proofpress for agent-native work by @chenmingtang830 in #14
• feat: add two-minute multi-format quickstart and CLI demos by @chenmingtang830 in #15
• docs: explain provenance ecosystem boundaries by @chenmingtang830 in #16
• chore: prepare Proofpress 0.3.0 by @chenmingtang830 in #17

Full Changelog: v0.2.0...v0.3.0