[HZ bands] inventory test

Tiers as horizontal bands (4 tier rows, containers laid out left-to-right within each):

flowchart TB
  subgraph frontG["Front tier"]
    direction LR
    web["`**web**
OpenResty (nginx + Lua)
_reverse proxy · rate/conn + bandwidth limits_
_serves /-/u/* uploads · publishes :80 :443_`"]
    cache["`**cache**
Redis 8.6.1 :6379
_presence · watchbar · login secrets_
_link-preview cache · auto-SSL storage_`"]
  end
  subgraph appG["App / data tier"]
    direction LR
    app["`**app**
JVM Java 11 · Play (Scala)
_talkyard-server :9000_
_React SSR in-JVM (Nashorn)_`"]
    rdb["`**rdb**
PostgreSQL 18.3 :5432
_all forum data_`"]
    search["`**search**
Elasticsearch 9.3.1 :9200
_full-text index_`"]
  end
  subgraph egrG["Egress"]
    direction LR
    egressp["`**egressp**
Smokescreen :4750
_SSRF-filtering egress proxy · read-only_`"]
  end
  subgraph idleG["Idle / on-demand"]
    direction LR
    rendr["`**rendr**
debian-slim
_placeholder — no traffic today_`"]
    backup["`**backup**
pg_dumpall + gpg
_profile-only · on-demand_`"]
  end
  classDef front fill:#dcfce7,stroke:#16a34a,color:#14532d
  classDef appt fill:#e0e7ff,stroke:#6366f1,color:#312e81
  classDef egr fill:#fee2e2,stroke:#dc2626,color:#7f1d1d
  classDef idle fill:#f3f4f6,stroke:#9ca3af,color:#4b5563,stroke-dasharray:5 5
  class web,cache front
  class app,rdb,search appt
  class egressp egr
  class rendr,backup idle

End.