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.

app_watchlist.go

@@ -200,6 +200,17 @@ func (a *App) watchSpot(dxCall, band, mode, country, comment string, freqHz int6
 	if !ok || !notify || a.ctx == nil {
 		return
 	}
+	// Already worked? Then nothing to announce. Judged HERE, before the sound —
+	// the report was an alert ringing for a slot the tab showed as Worked a
+	// moment later, because the frontend's verdict arrives on a debounce while
+	// the alert used to fire on the raw spot. Same verdict as the tab: exact
+	// slot for named modes, digital class for a generic DATA spot, today-only
+	// for a contest entry.
+	if e, found := a.watchlist.Get(entry); found {
+		if a.WatchlistWorkedSlots([]WatchlistSlotQuery{{Call: dxCall, Band: band, Mode: mode, Contest: e.IsContest}})[0] {
+			return
+		}
+	}
 	// Throttled per entry: a DXpedition lights up every skimmer on the planet,
 	// and forty alerts a minute for one station is a alarm nobody keeps on.
 	a.watchAlertMu.Lock()