Phase 3-5 of ActivityPub integration:
- Federation handlers: post.published, calendar_entry.created, product.listed
→ publish_activity() for AP outbox
- AP delivery handler: federation.activity_created → sign + POST to follower
inboxes with HTTP Signatures
- IPFS storage wired into publish_activity() (best-effort)
- Anchoring utility: merkle trees + OpenTimestamps Bitcoin timestamping
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
