3 gate-tier E2E tests:
- timeline-event-flow: binary data flow round-trip (no LLM)
- context-recovery-artifacts: seeded artifacts appear in preamble
- checkpoint-save-resume: checkpoint file created with YAML frontmatter
Also fixes package.json version sync (0.14.6.0 → 0.15.0.0).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>