feat(dashboard): expose trust reputation + reactions leaderboard

- GET /api/dashboard/reactions: top reacted messages (net add-remove),
  joined with message content, channel name, top 3 emoji breakdown
- Users tab: colored trust tier badge (Trusted/Netral/At Risk/Kritis)
  in list rows + detail panel (was plain number badge)
- Dashboard: new Reactions sub-tab with leaderboard
  (rank, emoji cluster, message, author, channel, count)

services/frontend/src/hooks/index.ts

@@ -4,6 +4,7 @@ export {
   useChannelDetail,
   useChannels,
   useStats,
+  useTopReactions,
   useUserDetail,
   useUsers,
 } from "./use-dashboard";