Add multi-provider event discovery and improve sync UI

backend/app/frontend/static/styles.css

@@ -143,6 +143,12 @@ h1 {
   line-height: 1.5;
 }
 
+.provider-summary {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 8px;
+}
+
 .dashboard-grid {
   display: grid;
   grid-template-columns: repeat(2, minmax(0, 1fr));
@@ -324,6 +330,33 @@ button:hover,
   color: var(--danger);
 }
 
+.provider-chip {
+  display: inline-flex;
+  align-items: center;
+  min-height: 32px;
+  padding: 0 12px;
+  border-radius: 999px;
+  background: rgba(46, 39, 30, 0.08);
+  color: var(--text);
+  font-family: var(--mono);
+  font-size: 0.78rem;
+}
+
+.provider-ticketmaster {
+  background: rgba(36, 94, 63, 0.12);
+  color: var(--success);
+}
+
+.provider-bandsintown {
+  background: rgba(194, 77, 44, 0.12);
+  color: var(--primary-dark);
+}
+
+.provider-eventim {
+  background: rgba(86, 60, 153, 0.14);
+  color: #4f3790;
+}
+
 .muted {
   color: var(--muted);
 }