fix: error-pages graded healthy, unwired sensors listed apart, Maintenance failed reads 0 (#5780, #5781, #5782)

- #5780 "The error-pages service is graded on other routers' errors". The
  Traefik scrape reads which services an errors middleware sends to, and
  grades them healthy: their 4xx and 5xx are the codes of the errors they
  cover for, already graded on the routers that failed.
- #5781 "The Maintenance failed rules sit at no data until a host has had
  a maintenance job". Every host with an agent reads 0 until a job fails.
- #5782 "VDNT-Util01's host page lists SYSTIN at 115 °C in red". The host
  page lists sensors that counts_as_hottest leaves out (unwired board
  inputs, 0 °C or below) on one muted line, not as heat.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/traefik/scraper.py

@@ -341,6 +341,32 @@ async def fetch_router_domains(base: str) -> dict[str, list[str]]:
     return out
 
 
+async def fetch_error_page_services(base: str) -> frozenset[str]:
+    """The services Traefik's `errors` middlewares send error pages to, named
+    as the metrics name them ("error-pages-service@swarm"). Such a service
+    answers with the code of the error it covers for: its 4xx and 5xx are
+    other routers' errors, already graded on them."""
+    async with httpx.AsyncClient(timeout=10.0) as client:
+        response = await client.get(f"{base}/http/middlewares", params={"per_page": 1000})
+        response.raise_for_status()
+        return error_page_services(response.json())
+
+
+def error_page_services(middlewares: list[dict]) -> frozenset[str]:
+    """fetch_error_page_services' reading of /api/http/middlewares: a service
+    named without a provider belongs to its middleware's provider."""
+    out = set()
+    for m in middlewares:
+        service = (m.get("errors") or {}).get("service")
+        if not service:
+            continue
+        if "@" not in service:
+            provider = m.get("provider") or (m.get("name", "").partition("@")[2])
+            service = f"{service}@{provider}" if provider else service
+        out.add(service)
+    return frozenset(out)
+
+
 def cert_names(cn: str | None, sans: str | None) -> set[str]:
     """Every name a certificate covers: its CN and SANs, lower-cased."""
     names = {n.strip().lower() for n in (sans or "").split(",") if n.strip()}