Split deploy into independent poller and web stacks

Decouple the privileged hardware poller from web iterations so a web
redeploy can never recreate/restart the poller (the backplane-touching
container). Two images from one Dockerfile via build targets:

- jbod-poller: privileged producer, ships smartmontools/sg3-utils/ledmon,
  Redis-only deps (~197MB)
- jbod-web: unprivileged read-only consumer (REST/UI/MQTT), no hardware
  tools, no /dev (~147MB)

Two compose projects sharing Redis over host networking:
- compose.infra.yml (jbod-infra): poller + redis — stable substrate
- compose.web.yml   (jbod-web):   app — 'up -d --build' touches only app

build.sh builds/pushes both images; split requirements-{poller,web}.txt;
dropped the combined docker-compose.yml; .dockerignore excludes tmp/ (keeps
the venv and the mqtt.env creds out of the build context).

requirements-web.txt

@@ -0,0 +1,6 @@
+# Web/API image — read-only consumer + MQTT. No hardware tools needed.
+fastapi>=0.115.0
+uvicorn>=0.34.0
+pydantic>=2.10.0
+redis>=5.0.0
+paho-mqtt>=2.1.0