docs: add TICKETMASTER_API_KEY to .env.example

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

.env.example

@@ -29,3 +29,8 @@ SQUID_QUALITY=mp3
 # 3. Copy the Client ID and Client Secret below
 SPOTIFY_CLIENT_ID=
 SPOTIFY_CLIENT_SECRET=
+
+# Ticketmaster Events (optional — free API key)
+# 1. Sign up at https://developer.ticketmaster.com/
+# 2. Create an app — copy the Consumer Key
+TICKETMASTER_API_KEY=