feat: add ATProto publishing, comments, and content tooling
Reposition library as a full ATProto longform publishing toolkit:
- Add write support via StandardSitePublisher (publish/update/delete)
- Introduce federated Bluesky comments component and utilities
- Add markdown → ATProto content transformation helpers
- Add verification helpers for .well-known and link tags
- Export schemas, collections, and new utility modules
Documentation overhaul:
- Rewrite README to focus on read + write workflows
- Add publishing, comments, verification, and transformation guides
- Clarify environment variables, security notes, and workflows
- Update examples and component docs
Developer experience:
- Add Vitest and test scripts
- Export new subpaths (publisher, content, comments, verification, schemas)
- Add Zod for schema validation
- Expand keywords to reflect federation and publishing