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/render_test.go

@@ -86,6 +86,7 @@ func TestTemplates_DashboardCriticalBadge(t *testing.T) {
 	type dashboardCustomer struct {
 		store.CustomerSummary
 		OverallStatus  string
+		HostCause      string
 		BackupAge      string
 		EventCriticals int
 		EventErrors    int