Switch transitions to Hasura streaming

[creatorrr]

trafficstars

Summary

• wire Hasura to docker-compose and reference JWT_SECRET
• document JWT secret env var
• drop SSE transitions stream route
• add Hasura metadata for transitions role
• add GraphQL queries for UI

Testing

• ruff format --check
• ruff check (fails: Fixes one unused-noqa)

Closes #1442