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/lib/api/dashboard.ts

@@ -5,6 +5,7 @@ import type {
   DashboardUserDetail,
   PaginatedChannels,
   PaginatedUsers,
+  TopReactedMessage,
 } from "@/lib/types";
 import { api } from "./client";
 
@@ -40,4 +41,7 @@ export const dashboardApi = {
 
   getChannelDetail: (channelId: string) =>
     api.get<DashboardChannelDetail>(`/api/dashboard/channels/${channelId}`),
+
+  getTopReactions: (limit = 20) =>
+    api.get<TopReactedMessage[]>(`/api/dashboard/reactions?limit=${limit}`),
 };