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/customer_unified.html

@@ -25,6 +25,7 @@
             <h1>
                 <span class="status-dot status-dot-{{statusColor .OverallStatus}}"></span>
                 {{if .CustomerName}}{{.CustomerName}}{{else}}{{.CustomerID}}{{end}}
+                {{if .HostCause}}<span class="status-badge status-badge-warn">{{.HostCause}}</span>{{end}}
             </h1>
             {{if .HasReports}}
             <p class="subtitle">
@@ -69,6 +70,7 @@
         <div class="summary-strip">
             <span class="strip-name">{{if .CustomerName}}{{.CustomerName}}{{else}}{{.CustomerID}}{{end}}</span>
             <span class="strip-item"><span class="status-dot status-dot-{{statusColor .OverallStatus}}"></span> {{.OverallStatus}}</span>
+            {{if .HostCause}}<span class="strip-item"><span class="status-badge status-badge-warn">{{.HostCause}}</span></span>{{end}}
             {{if .HasReports}}
             <span class="strip-item">Controller <code>{{.Customer.ControllerVersion}}</code></span>
             <span class="strip-item">Last report {{timeAgo .Customer.ReceivedAt}}</span>