ui+server: schedule next-run / last-run on dashboard + schedules tab

P2R-14. New store.LatestJobBySchedule query (per-schedule fired job).
Schedules-tab handler computes next-fire from cron + last-fire from
the jobs table per row. Schedules table grows two columns; dashboard
host row prepends 'next 12h ago/from now' to the existing last-backup
line when a single covering schedule is the run-now candidate.

Embeds store.Schedule into scheduleRow so existing template field
references keep working without bulk renames.

internal/server/http/schedule_nextrun_test.go

@@ -0,0 +1,48 @@
+// schedule_nextrun_test.go — pin the cron parser → next-run shape we
+// rely on for the dashboard host row + schedules tab (P2R-14).
+package http
+
+import (
+	"testing"
+	"time"
+)
+
+func TestCronParserNext(t *testing.T) {
+	cases := []struct {
+		name string
+		expr string
+		from time.Time
+		want time.Time
+	}{
+		{
+			name: "daily at 03:00",
+			expr: "0 3 * * *",
+			from: time.Date(2026, 5, 4, 1, 0, 0, 0, time.UTC),
+			want: time.Date(2026, 5, 4, 3, 0, 0, 0, time.UTC),
+		},
+		{
+			name: "daily at 03:00 (after time of day → next day)",
+			expr: "0 3 * * *",
+			from: time.Date(2026, 5, 4, 5, 0, 0, 0, time.UTC),
+			want: time.Date(2026, 5, 5, 3, 0, 0, 0, time.UTC),
+		},
+		{
+			name: "every 15 minutes",
+			expr: "*/15 * * * *",
+			from: time.Date(2026, 5, 4, 1, 7, 0, 0, time.UTC),
+			want: time.Date(2026, 5, 4, 1, 15, 0, 0, time.UTC),
+		},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			parsed, err := cronParser.Parse(c.expr)
+			if err != nil {
+				t.Fatalf("parse %q: %v", c.expr, err)
+			}
+			got := parsed.Next(c.from)
+			if !got.Equal(c.want) {
+				t.Fatalf("Next(%v) = %v, want %v", c.from, got, c.want)
+			}
+		})
+	}
+}