feat(status): what is wrong first — down monitors and active alerts, and since when (#5120)

#5120 "Status page: what is wrong first".

- A "Needs attention" card heads the Status board: each down monitor with
  how long it has been down, and each active alert (firing, acknowledged,
  pending, no data) with its condition and how long, linking to its history.
- StatusEntry.since / since_at_least: when the current up/down run began,
  from the recent checks (streak_start); "for at least" when every check we
  have agrees.
- Counts as stat tiles (Down, Active alerts, Pending, Up); names wrap
  instead of being cut off; dots carry their label.
- Uptime and TLS are coloured by status_class against Settings → Thresholds
  instead of literal cutoffs; heartbeat pills and DOWN/UP use tokens and
  status_badge rather than hex and bold.
- tests/core/test_status_page.py: streak_start cases, and the rows render
  with the problem card before the list, each since-time, threshold tones
  and no hex colour.

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

steward/core/status.py

@@ -38,6 +38,10 @@ class StatusEntry:
     spark_svg: str = ""             # filled by the route via sparkline_svg()
     tls_days: float | None = None   # days until TLS expiry (http only)
     detail_url: str | None = None
+    # When the current up/down state began, as far as the recent checks show;
+    # since_at_least means every check we have agrees, so it began earlier.
+    since: datetime | None = None
+    since_at_least: bool = False
 
 
 StatusSource = Callable[[object], Awaitable[list[StatusEntry]]]
@@ -158,6 +162,17 @@ async def _uptime_by_monitor(db, monitor_ids: list[str]) -> dict[str, dict]:
     return out
 
 
+def streak_start(results) -> tuple[datetime | None, bool]:
+    """(checked_at of the first check in the latest run of the same result,
+    whether that run fills every check given). Results are oldest-first."""
+    if not results:
+        return None, False
+    i = len(results) - 1
+    while i > 0 and results[i - 1].is_up == results[-1].is_up:
+        i -= 1
+    return results[i].checked_at, i == 0
+
+
 def _heartbeat_title(mtype: str, r) -> str:
     """Type-aware tooltip for one heartbeat cell."""
     ts = f"{r.checked_at:%H:%M:%S} UTC"
@@ -191,6 +206,7 @@ async def monitor_status_source(db) -> list[StatusEntry]:
         rows = recent.get(m.id, [])
         latest = rows[-1] if rows else None
         status = "pending" if latest is None else ("up" if latest.is_up else "down")
+        since, since_at_least = streak_start(rows)
         tls_days = None
         if latest and latest.tls_expires_at:
             tls_days = (latest.tls_expires_at - now).total_seconds() / 86400.0
@@ -203,5 +219,6 @@ async def monitor_status_source(db) -> list[StatusEntry]:
             latency_ms=latest.response_ms if latest else None,
             spark=[r.response_ms for r in rows if r.response_ms is not None],
             tls_days=tls_days, detail_url="/monitors/",
+            since=since, since_at_least=since_at_least,
         ))
     return entries