perf: cache Ticketmaster event results for 30 min per artist

Avoids burning API quota on repeat visits to the same artist page.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/views/events.js

@@ -1,14 +1,21 @@
 import { esc } from '../utils.js';
 import { S } from '../state.js';
 
+// Cache results for the session — keyed by artist name, expires after 30 min.
+const _cache = new Map(); // name → { ts, data }
+const _TTL   = 30 * 60 * 1000;
+
 export async function fetchEvents(artistName) {
   const base = S.cfg?.backendUrl;
   if(!base) return [];
+  const hit = _cache.get(artistName);
+  if(hit && Date.now() - hit.ts < _TTL) return hit.data;
   try {
     const r = await fetch(`${base}/api/events/${encodeURIComponent(artistName)}`);
     if(!r.ok) return [];
     const data = await r.json();
     if(!Array.isArray(data)) return [];
+    _cache.set(artistName, { ts: Date.now(), data });
     return data;
   } catch { return []; }
 }