Split into dedicated hardware poller + read-only consumers

Rearchitect so a single poller process is the sole owner of all SAS/SMART/
SES hardware I/O, serialized behind one gate and paced, writing results to
Redis. The API/web and MQTT publisher become pure Redis readers — they no
longer issue any subprocess and can restart freely without touching the bus.

This addresses backplane/expander stress from concurrent + restart-triggered
SMART/SES storms (the prior model re-ran a hardware sweep on every container
start, and polled sg_ses 0x02+0x07 every 60s; 0x07 errored on the IOM6/
Xyratex expanders).

- poller.py: paced sweep (inventory, SMART per-drive w/ gap, SES 0x02, ZFS,
  host/MegaRAID), startup jitter, single-instance Redis lock, LED-queue worker
- services/hwgate.py: global serialization semaphore (POLL_CONCURRENCY=1)
- services/store.py: Redis as the only producer<->consumer interface + LED queue
- services/health.py: shared drive-health classifier (fixes overview double-count)
- gate smartctl/sg_ses/zpool/ledctl; drop sg_ses 0x07 from the hot path
- routers + temps read-only from the store; main.py drops the in-process poller
- compose: 3 services (privileged poller + unprivileged app + redis) w/ pacing knobs

routers/leds.py

@@ -1,7 +1,9 @@
+import re
+
 from fastapi import APIRouter, HTTPException
 from pydantic import BaseModel, field_validator
 
-from services.leds import set_led
+from services import store
 
 router = APIRouter(prefix="/api/drives", tags=["leds"])
 
@@ -19,11 +21,12 @@ class LedRequest(BaseModel):
 
 @router.post("/{device}/led")
 async def set_drive_led(device: str, body: LedRequest):
-    """Set the locate LED for a drive."""
-    try:
-        result = await set_led(device, body.state)
-    except ValueError as e:
-        raise HTTPException(status_code=400, detail=str(e))
-    except RuntimeError as e:
-        raise HTTPException(status_code=502, detail=str(e))
-    return result
+    """Queue a locate-LED change. The poller (sole hardware owner) executes it."""
+    if not re.fullmatch(r"[a-zA-Z0-9]+", device):
+        raise HTTPException(status_code=400, detail=f"Invalid device name: {device}")
+
+    queued = await store.enqueue_led(device, body.state)
+    if not queued:
+        raise HTTPException(status_code=503, detail="LED queue unavailable (Redis down)")
+
+    return {"device": device, "state": body.state, "queued": True}