Add HTTP caching headers (ETag / Cache-Control)

[lukesmmr]

Context

The API currently has no HTTP caching — every request hits PostgreSQL directly. The mobile app polls every 60 seconds in the foreground, meaning frequent identical queries.

Proposed Change

Add caching headers to read endpoints:

Endpoint	Strategy	TTL
GET /api/v1/disasters	Cache-Control: public, max-age=30	30s
GET /api/v1/disasters/near	Cache-Control: public, max-age=30	30s
GET /api/v1/disasters/:id	ETag based on updated_at	Revalidate
GET /healthz	Cache-Control: no-cache	—

This reduces database load and improves mobile app responsiveness. Short TTLs (30s) still provide near-real-time data while cutting redundant queries.

Future

Consider Redis for query-level caching when traffic warrants it.

Labels

enhancement, performance