ui(relTime): tick relative timestamps client-side so long-open tabs don't freeze

formatRelTime now wraps its label in <time data-rel-ts=...>, and
both layouts include a small ticker that re-renders every 30s.
Without this, a job-detail page rendered an hour ago kept showing
'2h ago' when the wall-clock truth was '3h ago'.

internal/server/ui/funcs_test.go

@@ -0,0 +1,49 @@
+package ui
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestFormatRelTimeWrapsInTickableTimeElement(t *testing.T) {
+	// A long-open tab needs a stable anchor so the JS ticker can
+	// refresh the label — see base.html.
+	when := time.Now().Add(-3 * time.Hour)
+	got := string(formatRelTime(when))
+	if !strings.Contains(got, `<time data-rel-ts="`) {
+		t.Errorf("missing data-rel-ts anchor in %q", got)
+	}
+	if !strings.Contains(got, "3h ago</time>") {
+		t.Errorf("expected '3h ago' label, got %q", got)
+	}
+}
+
+func TestFormatRelTimeNilReturnsDash(t *testing.T) {
+	var p *time.Time
+	if string(formatRelTime(p)) != "—" {
+		t.Errorf("nil should render as em-dash, got %q", formatRelTime(p))
+	}
+	if string(formatRelTime(time.Time{})) != "—" {
+		t.Errorf("zero should render as em-dash")
+	}
+}
+
+func TestRelTimeLabelBuckets(t *testing.T) {
+	cases := []struct {
+		d    time.Duration
+		want string
+	}{
+		{30 * time.Second, "30s ago"},
+		{5 * time.Minute, "5m ago"},
+		{2 * time.Hour, "2h ago"},
+		{3 * 24 * time.Hour, "3d ago"},
+		{2 * 7 * 24 * time.Hour, "2w ago"},
+		{-5 * time.Minute, "5m from now"},
+	}
+	for _, c := range cases {
+		if got := relTimeLabel(c.d); got != c.want {
+			t.Errorf("relTimeLabel(%v) = %q, want %q", c.d, got, c.want)
+		}
+	}
+}