feat(monitoring): add Redis exporter + Sentry docs to deployment guide

- Add redis-exporter container to docker-compose (oliver006/redis_exporter, 32MB)
- Add Redis scrape target to Prometheus config
- Add 4 Redis alert rules: RedisDown, HighMemory, HighConnections, RejectedConnections
- Document Step 19b (Sentry Error Tracking) in Hetzner deployment guide
- Document Step 19c (Redis Monitoring) in Hetzner deployment guide
- Update resource budget and port reference tables

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

requirements-test.txt

@@ -8,4 +8,4 @@ pytest-json-report>=1.5.0
 httpx>=0.28.1
 faker>=33.1.0
 pytest-repeat>=0.9.4
-pytest-timeout>=2.3.1
+pytest-timeout>=2.3.1