feat(watchlist): confirm an add, and both messages clear themselves

A green line under the toolbar says what was added (and as what — the contest
variant names the per-UTC-day rule); the already-exists error keeps its red
line. Both fade after four seconds: a stale 'added' from ten minutes ago reads
as a fresh one.

frontend/src/components/WatchlistTab.tsx

@@ -84,6 +84,16 @@ export function WatchlistTab({ spots, spotStatus, onSpotSelect, onSpotClick }: P
     return m === modeFilter;
   };
   const [error, setError] = useState('');
+  // A quiet confirmation under the toolbar; both messages clear themselves —
+  // a stale "added" from ten minutes ago reads as a fresh one.
+  const [notice, setNotice] = useState('');
+  const noticeTimer = useRef<number | undefined>(undefined);
+  const flash = (msg: string, isError: boolean) => {
+    if (noticeTimer.current) window.clearTimeout(noticeTimer.current);
+    setError(isError ? msg : '');
+    setNotice(isError ? '' : msg);
+    noticeTimer.current = window.setTimeout(() => { setError(''); setNotice(''); }, 4000) as unknown as number;
+  };
   const [removeArm, setRemoveArm] = useState('');
   // worked answer per "call|band|modeclass|contest" key.
   const [worked, setWorked] = useState<Record<string, boolean>>({});
@@ -168,9 +178,12 @@ export function WatchlistTab({ spots, spotStatus, onSpotSelect, onSpotClick }: P
   const add = async () => {
     const c = addCall.trim().toUpperCase();
     if (!c) return;
-    setError('');
-    try { await WatchlistAdd(c, addContest); setAddCall(''); await refresh(); }
-    catch (e: any) { setError(String(e?.message ?? e)); }
+    try {
+      await WatchlistAdd(c, addContest);
+      setAddCall('');
+      flash(t(addContest ? 'wl.addedContest' : 'wl.added', { call: c }), false);
+      await refresh();
+    } catch (e: any) { flash(String(e?.message ?? e), true); }
   };
 
   const remove = async (call: string) => {
@@ -296,6 +309,7 @@ export function WatchlistTab({ spots, spotStatus, onSpotSelect, onSpotClick }: P
         </div>
       </div>
       {error && <div className="text-xs text-danger px-1">{error}</div>}
+      {notice && <div className="text-xs text-success px-1">{notice}</div>}
 
       {/* cards */}
       <div className="flex-1 min-h-0 overflow-y-auto space-y-2 pr-1">

frontend/src/lib/i18n.tsx

@@ -39,7 +39,7 @@ const en: Dict = {
   'cwd.tipOnIdle': 'CW decoder — on, idle until CW mode · click to disable',
   'cwd.tipOff': 'CW decoder · click to enable (decodes RX audio in CW mode)',
   'tools.watchlist': 'Watchlist…', 'tab.watchlist': 'Watchlist',
-  'wl.addPh': 'Callsign or VK9*', 'wl.add': 'Add', 'wl.contest': 'Contest', 'wl.addAsContest': 'as contest', 'wl.cTotal': 'Watchlist:', 'wl.cActive': 'Active:', 'wl.cNeeded': 'Needed:', 'wl.allModes': 'All modes', 'wl.modeFilter': 'Only show spots in this mode', 'wl.patternPh': 'Auto contest (e.g. WWA)', 'wl.patternHint': 'Auto-add as contest: any spotted callsign CONTAINING this text joins the watchlist as a contest entry by itself. Empty = off; collected entries stay.',
+  'wl.addPh': 'Callsign or VK9*', 'wl.added': '{call} added to the watchlist.', 'wl.addedContest': '{call} added as a contest entry (judged per UTC day).', 'wl.add': 'Add', 'wl.contest': 'Contest', 'wl.addAsContest': 'as contest', 'wl.cTotal': 'Watchlist:', 'wl.cActive': 'Active:', 'wl.cNeeded': 'Needed:', 'wl.allModes': 'All modes', 'wl.modeFilter': 'Only show spots in this mode', 'wl.patternPh': 'Auto contest (e.g. WWA)', 'wl.patternHint': 'Auto-add as contest: any spotted callsign CONTAINING this text joins the watchlist as a contest entry by itself. Empty = off; collected entries stay.',
   'wl.contestHint': 'Contest station: worked/needed is judged against the current UTC day — at 00:00 UTC every slot can be worked again.',
   'wl.searchPh': 'Search…', 'wl.famAll': 'All', 'wl.famNormal': 'DX', 'wl.famContest': 'Contest',
   'wl.activeOnly': 'Active', 'wl.neededOnly': 'Needed',
@@ -563,7 +563,7 @@ const fr: Dict = {
   'cwd.tipOnIdle': 'Décodeur CW — actif, en veille hors mode CW · clic pour désactiver',
   'cwd.tipOff': 'Décodeur CW · clic pour activer (décode l’audio RX en mode CW)',
   'tools.watchlist': 'Watchlist…', 'tab.watchlist': 'Watchlist',
-  'wl.addPh': 'Indicatif ou VK9*', 'wl.add': 'Ajouter', 'wl.contest': 'Contest', 'wl.addAsContest': 'comme contest', 'wl.cTotal': 'Watchlist :', 'wl.cActive': 'Actives :', 'wl.cNeeded': 'Manquantes :', 'wl.allModes': 'Tous les modes', 'wl.modeFilter': 'Ne montrer que les spots de ce mode', 'wl.patternPh': 'Auto contest (ex. WWA)', 'wl.patternHint': "Ajout auto comme contest : tout indicatif spotté CONTENANT ce texte rejoint la watchlist en entrée contest tout seul. Vide = désactivé ; les entrées déjà collectées restent.",
+  'wl.addPh': 'Indicatif ou VK9*', 'wl.added': '{call} ajouté à la watchlist.', 'wl.addedContest': '{call} ajouté en entrée contest (jugée par jour UTC).', 'wl.add': 'Ajouter', 'wl.contest': 'Contest', 'wl.addAsContest': 'comme contest', 'wl.cTotal': 'Watchlist :', 'wl.cActive': 'Actives :', 'wl.cNeeded': 'Manquantes :', 'wl.allModes': 'Tous les modes', 'wl.modeFilter': 'Ne montrer que les spots de ce mode', 'wl.patternPh': 'Auto contest (ex. WWA)', 'wl.patternHint': "Ajout auto comme contest : tout indicatif spotté CONTENANT ce texte rejoint la watchlist en entrée contest tout seul. Vide = désactivé ; les entrées déjà collectées restent.",
   'wl.contestHint': "Station contest : contacté/manquant est jugé sur la journée UTC courante — à 00:00 UTC chaque créneau redevient à faire.",
   'wl.searchPh': 'Chercher…', 'wl.famAll': 'Tous', 'wl.famNormal': 'DX', 'wl.famContest': 'Contest',
   'wl.activeOnly': 'Actifs', 'wl.neededOnly': 'Manquants',