feat(email-threads-api): implement Email Threads API for bounty #4

[3894226862-benben]

Implementation: Email Threads API

This PR implements the Email Threads API bounty (#4, ).

Complete implementation includes:

Backend

• Express.js server with TypeScript
• Prisma ORM with PostgreSQL schema (User, Thread, Message, ThreadParticipant, ThreadRead)
• Full API endpoints: list threads, get thread, save draft, archive, delete
• Input validation, error handling, and logging
• JWT-based auth integration ready

API Endpoints

Method	Path	Description
GET	/api/threads	List threads (paginated, searchable, filterable)
GET	/api/threads/:id	Get thread detail with all messages
POST	/api/threads/:id/drafts	Create/update draft in thread
PUT	/api/threads/:id/archive	Archive thread
DELETE	/api/threads/:id	Soft-delete thread

Testing & Documentation

• Jest unit tests (auth, ordering, filters, drafts)
• Swagger/OpenAPI docs
• Docker setup with docker-compose
• Full README with API reference

Skills Demonstrated

• Node.js/TypeScript
• Express.js API development
• Prisma ORM
• PostgreSQL
• Jest testing
• Docker
• API design

Full source code: https://github.com/3894226862-benben/email-threads-api