feat(watchlist): header counters, mode filter — and the alert checks worked FIRST

DXHunter's header row, ported: Watchlist / Active / Needed counts up front and
the All-Modes select beside the other filters (DIGI matches the digital class,
SSB folds USB/LSB). Counters, card lists and the Active/Needed-only filters all
read the same mode-filtered view, so the numbers add up to what is on screen.

And the notify alert now asks the SAME worked-slot question the tab asks —
before making a sound. It used to fire on the raw spot while the tab's verdict
arrived on a debounce, so the bell rang for a slot that showed Worked a moment
later. Judged in the backend at emit time: exact slot for named modes, digital
class for generic DATA, today-only for contest entries.

internal/watchlist/watchlist.go

@@ -234,3 +234,15 @@ func lastSeenLabel(t time.Time) string {
 		return fmt.Sprintf("%dd ago", int(d.Hours()/24))
 	}
 }
+
+// Get returns one entry by its exact name — the alert path needs its contest
+// flag after MarkSeen named it.
+func (s *Store) Get(callsign string) (Entry, bool) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	e, ok := s.entries[strings.ToUpper(strings.TrimSpace(callsign))]
+	if !ok {
+		return Entry{}, false
+	}
+	return *e, true
+}