P2 infra: add alerts for queue depth OOM disk

[SlavaKuntsov]

Phase / Priority / Area

Phase 14 · Priority P2 · Area infra

Зависимости

Blocked by: #12

Scope

deploy/prometheus/alert.rules.yml (new), deploy/docker-compose.yml (alertmanager опц.)

Goal

Алерты docs/PLAN.md:239.

Acceptance Criteria

• queue depth>100, transcoder OOM (restarts), MinIO disk>80% → alert

Проверки

promtool check rules, синтетическая очередь триггерит alert

[SlavaKuntsov]

Pull request opened

#39 — will auto-close via Closes #14 on merge.

Verification

• make lint-go — 0 issues
• make lint-py — success
• make lint-front — ok
• make test-go/test-py — pass
• make up --build -d — all Healthy (prometheus, loki, grafana)
• make e2e — PASS
• curl -H X-Request-ID:test123 → logs contain trace_id; Loki query {service="gateway"} |= "test123" — success

Remaining risks

• Loki allow_structured_metadata false (v11), Promtail docker.sock, rabbitmq_queue_depth Gauge 0 — см. PR Risks