hive-c0re: replace the agents_crashing banner with a crash-watcher log line + grafana alert

docs/web-ui/dashboard.md

@@ -40,9 +40,13 @@ from the dashboard tab strip.
   that registry. Producers today include the host disk-pressure check
   (a `statvfs` probe of `/nix`: ≥85% used → `warn`, ≥95% → `crit`, e.g.
   `⚠ host nix store N% full (G GiB free) — garbage-collect …`), forge
-  provisioning/CI-runner boot failures, and agent-state warnings
-  (`pending_logins`, `agents_crashing`) computed alongside the container
-  snapshot. Hidden when there are no warnings.
+  provisioning/CI-runner boot failures, and an agent-state warning
+  (`pending_logins`) computed alongside the container snapshot. A
+  container crash used to have a sibling `agents_crashing` entry here —
+  removed in favour of a swarm-level grafana alert on the crash
+  watcher's own log line (`docs/scheduler/observability.md`), so a
+  hive with no otel export now has no operator-visible crash signal at
+  all. Hidden when there are no warnings.
 - **Browser tab title** — `hyperhive // h1ve-c0re` by default; updated
   to `<swarm> / <hive> // h1ve-c0re` once `hive_name` / `swarm_name`
   arrive in the state snapshot.