api: health endpoint logs Redis failures at error level, masking real errors

[distroinfinity]

packages/api/src/routes/health.ts:9 — toComponentStatus logs all probe failures at error level. Since Redis is non-fatal (fail-open by design), every Redis outage generates error-level log noise every 30s. Makes it hard to distinguish real errors from expected degradation.

Fix: pass a severity parameter and use warn for Redis, error for DB.

AC: Redis probe failures log at warn, DB probe failures log at error.