Isochrone Provider Integration & Redis Caching

[hoangsonww]

Summary
Generate travel-time polygons via a pluggable provider (Mapbox, OpenRouteService, Google) and cache by normalized request hash to meet latency goals.

Acceptance Criteria

• POST /api/commute/isochrone returns GeoJSON polygon(s) for { destinations[], mode, window, minutes }.
• Requests normalized and hashed; cached results returned when available.
• P95 cached response ≤ 5s; cold path ≤ 10s on happy path.
• Rate limiting and retry/backoff with exponential jitter.

Tasks

• Provider abstraction + config flags
• Request normalization + hashing
• Redis get/set with TTL; metrics on hit ratio
• Error mapping to user-friendly messages
• Unit tests: hashing, caching, retries