fix: plug memory leaks in blob URLs and traffic cache

- Add URL.revokeObjectURL on unmount and media removal in
  AdminBroadcastCreate, AdminPinnedMessageCreate, Support
- Track blob URLs via refs to revoke before creating new ones
- Add clearCreateAttachment/clearReplyAttachment helpers in Support
  to properly revoke blob URLs when clearing attachments
- Cap adminTraffic cache at 20 entries with FIFO eviction to prevent
  unbounded memory growth from different filter combinations

src/api/adminTraffic.ts

@@ -63,6 +63,7 @@ export type TrafficParams = {
 };
 
 const CACHE_TTL = 5 * 60 * 1000; // 5 minutes
+const MAX_CACHE_ENTRIES = 20;
 
 const trafficCache = new Map<string, { data: TrafficUsageResponse; timestamp: number }>();
 
@@ -106,6 +107,16 @@ export const adminTrafficApi = {
 
     trafficCache.set(key, { data, timestamp: Date.now() });
 
+    // Evict oldest entries to prevent unbounded memory growth
+    if (trafficCache.size > MAX_CACHE_ENTRIES) {
+      const iterator = trafficCache.keys();
+      while (trafficCache.size > MAX_CACHE_ENTRIES) {
+        const oldest = iterator.next();
+        if (oldest.done) break;
+        trafficCache.delete(oldest.value);
+      }
+    }
+
     return data;
   },