feat(widgets): Routers and Hosts problem rows say since when (#5810)

Routers: a router in trouble reads 'started 2h ago' or 'all of the last
24 h', from problem_since over the day's history, read for the troubled
routers only (a certificate's problem carries its own date). Hosts: a
down host reads 'a monitor is down for 3h'; host_glance keeps the
down_since host_status already had.

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

steward/hosts/service.py

@@ -373,7 +373,7 @@ GLANCE_ORDER = {"down": 0, "crit": 1, "stale": 2, "warn": 3, "up": 4, "unknown":
 def host_glance(hosts, status: dict, agent: dict, thresholds: dict) -> list[dict]:
     """The Hosts — Overview rows, worst first (#5251).
 
-    Each is {host, state, worst, agent}. State is "down" when a linked monitor
+    Each is {host, state, worst, agent, down_since}. State is "down" when a linked monitor
     is down, "stale" when the agent has stopped reporting, else the grade of
     the reading furthest past its cutoff ("crit" / "warn": CPU, memory, disk /
     or load per core, against Settings → Thresholds; CPU, memory and load
@@ -406,5 +406,6 @@ def host_glance(hosts, status: dict, agent: dict, thresholds: dict) -> list[dict
             state = "up"
         else:
             state = "unknown"
-        rows.append({"host": h, "state": state, "worst": worst, "agent": a or {}, "grades": grades})
+        rows.append({"host": h, "state": state, "worst": worst, "agent": a or {}, "grades": grades,
+                     "down_since": st.get("down_since") if state == "down" else None})
     return sorted(rows, key=lambda r: (GLANCE_ORDER[r["state"]], r["host"].name.lower()))