Boron Context v0.7.8: vision-grounded repository retrieval

[kforris]

Summary

• add bounded Markdown retrieval from confirmed registered project roots
• query all live adapters before snapshot fallback and disambiguate read-only high-risk language
• add an 18-case production-shaped repository evaluation and v0.7.8 documentation

Verification

• npm run check
• npm run format:check
• npm audit --omit=dev --audit-level=high
• npm pack --dry-run
• temporary PostgreSQL 17 migration, 13/13 integration tests, repeat migration
• Swift 5/5 tests and release build

Product boundary

This PR does not make Boron Context a release candidate and does not authorize a public release or Marketplace submission. Live eligible source coverage and the separate 0.8 lifecycle rehearsal remain open gates.