Obligation-First v0.4.2

Correctness patch: JSON-LD @context resolution, release-URL 404 fix, validators fail on missing dirs, plus schema-field and publishing-surface reconciliation.

• manifest.json - machine-readable release package manifest
• sha256.txt - SHA-256 checksum index
• RELEASE_NOTES-v0.4.2.md - release notes and verification summary
• /v1/context.jsonld - JSON-LD context
• /v1/schema/ - JSON Schemas
• /.well-known/assistant-guide.txt - GuideCheck assistant guide

Full changelog