[PBI] Documentation and Diagrams

[jinseisieko]

Description & Context

Create comprehensive documentation including architecture.md, api.md, websocket_protocol.md, and deployment.md. Fill in OpenAPI descriptions for all REST endpoints. Draw PlantUML diagrams for data_flow.puml and subscription_lifecycle.puml to visualize system architecture and protocols.

Acceptance Criteria

AC 1

• Given the API documentation is viewed, When OpenAPI specs are rendered, Then all REST endpoints are fully described with request/response schemas.

AC 2

• Given the WebSocket protocol document is read, When reviewing the lifecycle, Then all JSON control messages and close codes (4001-4004) are clearly documented.

AC 3

• Given the PlantUML diagrams are rendered, When viewing data_flow.puml and subscription_lifecycle.puml, Then they accurately reflect the system's data paths and state transitions.

Assigned Reviewer

@Minnezing