dashboard, status API and notifications tell apex domains from hostnames (closes #224)

An apex domain's own records are still saved with the hostnames'
records, under the domain's name, so the port and TLS checks find its
addresses. Notifications about them now start `Domain:`, decided by the
configured domains. The dashboard and /api/v1/status, which read only
the saved state, take a hostname entry whose name also has a domain
entry as that domain's own records: the dashboard shows them in a second
table under Domains, the API in the domain's `recordsByNameserver`, and
neither lists or counts them as hostnames. The startup notification
counts domains and hostnames from the configuration. README says which
of a domain's own records are watched and how their changes are
notified.

Model: opus-5-5

internal/handlers/dashboard_test.go

@@ -1,6 +1,7 @@
 package handlers_test
 
 import (
+	"regexp"
 	"strings"
 	"testing"
 	"time"
@@ -154,3 +155,53 @@ func TestDashboardShowsFailureReasons(t *testing.T) {
 		t.Errorf("row of %s does not show %q", certKey, certFailedReason)
 	}
 }
+
+// dashboardSection returns the section of page under heading.
+func dashboardSection(t *testing.T, page string, heading string) string {
+	t.Helper()
+
+	for section := range strings.SplitSeq(page, "<section") {
+		words := strings.Join(strings.Fields(section), " ")
+		if strings.Contains(words, "> "+heading+" </h2>") {
+			return section
+		}
+	}
+
+	t.Fatalf("dashboard has no section headed %q", heading)
+
+	return ""
+}
+
+// TestDashboardShowsDomainRecordsUnderDomains checks that the dashboard
+// shows an apex domain's own records in the Domains section, and
+// neither lists nor counts the domain as a hostname.
+func TestDashboardShowsDomainRecordsUnderDomains(t *testing.T) {
+	t.Parallel()
+
+	page := get(t, newHandlersWithFailures(t).HandleDashboard())
+
+	domains := dashboardSection(t, page, "Domains")
+	if !strings.Contains(dashboardRow(t, domains, domainAddress), testDomain) {
+		t.Errorf("row of %s does not name %s", domainAddress, testDomain)
+	}
+
+	if strings.Contains(dashboardSection(t, page, "Hostnames"), testDomain) {
+		t.Errorf("Hostnames section lists the domain %s", testDomain)
+	}
+
+	words := strings.Join(strings.Fields(page), " ")
+
+	footer := "monitoring 1 domains + 1 hostnames"
+	if !strings.Contains(words, footer) {
+		t.Errorf("dashboard does not say %q", footer)
+	}
+
+	// With the tags taken out, the summary bar starts "Domains 1
+	// Hostnames 1".
+	text := regexp.MustCompile(`<[^>]*>`).ReplaceAllString(page, " ")
+	summary := "Domains 1 Hostnames 1"
+
+	if !strings.Contains(strings.Join(strings.Fields(text), " "), summary) {
+		t.Errorf("summary bar does not say %q", summary)
+	}
+}