hub: dead-host roll-up honesty - customer status folds worst expected host

Customer status (dashboard row, /configs list, detail header + strip) is
now worst(controllerDerived, hostStatusOf(each expected host)) via the ONE
staleness definition (Server.hostStatus, hosts.go - shared with the
HostStalenessChecker; no second threshold). Any host down/stale caps the
customer at WARN with a cause chip naming the host ("host down: <id>");
pending (never-reported) hosts worsen only once the customer has reported
(onboarding exclusion). The three previously-inlined controller-status
chains collapse into controllerStatus() (rollup.go). Display + derivation
only - checker alerting untouched.

Live shape pinned (drill-1 / Peti cluster): host down 23h + controller
report minutes old rendered a GREEN row - TestRollup_DeadHostMasking now
fails that exact outcome. Red-proof: short-circuiting foldHostStatus to
controller-only flips C + two D subtests red ("dashboard row is GREEN
over a 23h-dead host").

hub/internal/web/templates/dashboard.html

@@ -54,6 +54,7 @@
                         <span class="status-badge status-badge-{{.OverallStatus}}">
                             {{if eq .OverallStatus "ok"}}OK{{else if eq .OverallStatus "warn"}}WARN{{else if eq .OverallStatus "disabled"}}PAUSED{{else if eq .OverallStatus "pending"}}PENDING{{else}}DOWN{{end}}
                         </span>
+                        {{if .HostCause}}<span class="status-badge status-badge-warn">{{.HostCause}}</span>{{end}}
                     </td>
                     <td>{{if eq .OverallStatus "pending"}}—{{else}}{{if gt (add (add .EventCriticals .EventErrors) .EventWarnings) 0}}{{if gt .EventCriticals 0}}<span class="severity-badge severity-critical">{{.EventCriticals}}</span>{{end}}{{if gt .EventErrors 0}}<span class="severity-badge severity-error">{{.EventErrors}}</span>{{end}}{{if gt .EventWarnings 0}}<span class="severity-badge severity-warning">{{.EventWarnings}}</span>{{end}}{{else}}<span class="text-muted">—</span>{{end}}{{end}}</td>
                     <td>{{if eq .OverallStatus "pending"}}—{{else}}{{timeAgo .ReceivedAt}}{{end}}</td>