fix(voice): proper shadcn select dropdowns + top reactors leaderboard

- ui/select: trigger default w-full h-9 (was w-fit h-8 — selects rendered
  tiny/misaligned); callers keep size override via className
- VoiceConnectionCard: labeled full-width h-10 selects (Server/Guild +
  Voice Channel), guild icon + name in options, channel type icon +
  'no akses' tag, empty states, htmlFor/id a11y wiring
- GuildSelector sidebar + messages channel filter bumped to match
- Backend GET /api/dashboard/reactors: top users by net reactions given
  (adds-removes) + messages_reacted + emojis_used
- Reactions tab: second 'Top reaktor' leaderboard panel

services/backend/src/modules/dashboard/dashboard.service.ts

@@ -48,6 +48,11 @@ export class DashboardService {
     logger.debug({ limit }, "Fetching top reactions");
     return dashboardRepository.getTopReactions(limit);
   }
+
+  async getTopReactors(limit: number) {
+    logger.debug({ limit }, "Fetching top reactors");
+    return dashboardRepository.getTopReactors(limit);
+  }
 }
 
 export const dashboardService = new DashboardService();