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>

tests/plugins/host_agent/test_expand_metrics.py

@@ -156,3 +156,13 @@ def test_the_registration_keeps_the_host_s_updates_and_reboot():
                         "reboot": {"required": False}}, now)
     assert reg.updates_pending == 4 and reg.updates_error == "apt is locked"
     assert reg.reboot_required is False and reg.reboot_required_since is None
+
+
+def test_the_page_lists_unwired_sensors_apart_hottest_first():
+    """VDNT-Util01's sensor list read SYSTIN 115 °C in red at the top, though
+    the host's temperature already left it out (#5759)."""
+    from plugins.host_agent.routes import split_temps
+    real, unwired = split_temps({"SYSTIN": 115.0, "AUXTIN0": 110.0, "Package id 0": 52.0,
+                                 "Composite": 48.9, "PCH_CHIP_TEMP": 0.0, "CPUTIN": 47.0, "gone": None})
+    assert list(real) == ["Package id 0", "Composite", "CPUTIN", "gone"]
+    assert list(unwired) == ["SYSTIN", "AUXTIN0", "PCH_CHIP_TEMP"]