feat(watchlist): exact match by default, * for a family

The prefix matching ported from DXHunter swallowed too much: a three-letter
special-event entry N8W lit up NEEDED for N8WCR, a different station entirely.
The implicit becomes explicit — a bare entry matches exactly that call, a
trailing star makes it a family: VK9* catches every VK9…, RI0SP* the
expedition's portable forms. A star anywhere else (or alone) is refused at Add
rather than silently matching nothing. Same rule in the backend Match and the
tab's own matcher, pinned by test.

frontend/src/components/WatchlistTab.tsx

@@ -43,9 +43,16 @@ interface Props {
 // A spot is ON AIR for the badge while its last sighting is this fresh.
 const ON_AIR_MS = 10 * 60 * 1000;
 
+// Exact unless the entry carries a trailing * — the same rule the backend's
+// Match applies to the live stream, mirrored so the tab and the alerts can
+// never disagree about what an entry covers.
 function matchesEntry(call: string, pattern: string): boolean {
   const c = call.toUpperCase();
-  return c === pattern || c.startsWith(pattern);
+  if (pattern.endsWith('*')) {
+    const p = pattern.slice(0, -1);
+    return p !== '' && c.startsWith(p);
+  }
+  return c === pattern;
 }
 
 export function WatchlistTab({ spots, spotStatus, onSpotSelect, onSpotClick }: Props) {