[Feature] OpenAPI specification and auto-generated docs

[Siddhant-K-code]

Summary

Add an OpenAPI 3.1 spec for all API endpoints and serve interactive docs via Swagger UI.

Motivation

An OpenAPI spec signals production readiness and enables:

• Auto-generated client SDKs (Python, TypeScript, etc.)
• Interactive API explorer at /docs
• Import into Postman, Insomnia, and other tools
• Accurate documentation that stays in sync with code

Endpoints to document

Method	Path	Description
POST	/v1/dedupe	Deduplicate chunks
POST	/v1/dedupe/stream	SSE streaming dedup
POST	/v1/retrieve	Query vector DB with dedup
GET	/health	Health check
GET	/metrics	Prometheus metrics

Deliverables

• openapi.yaml at repo root
• Serve Swagger UI at GET /docs (embed via swaggo/http-swagger or static HTML)
• Request/response schemas with examples
• Auth scheme documented (Bearer token)
• Error response schemas (400, 401, 500)
• CI check that validates spec against implementation

Acceptance Criteria

• GET /docs renders interactive API explorer
• All endpoints have request/response examples
• Spec validates with swagger-cli validate
• Can generate a working Python client from the spec