feat: replace corrections/tuner with dashboard module

Replace the corrections/adaptive-prompt-tuner feature with a new
dashboard module providing server stats and user profile overview.

Backend:
- Add dashboard module (routes, service, repository) with stats + user list + user detail endpoints
- Remove corrections module entirely
- Wire dashboard router in app.ts

Frontend:
- Add dashboard feature (DashboardStats, UserSummaryList, UserProfileDetail components + useDashboard hook)
- Remove tuner feature (CorrectionStats, CorrectionHistory, SubmitCorrection, useCorrections)
- Update API client from corrections → dashboard types/fns
- Rename tab 'tuner' → 'dashboard'
- Update MobileTabBar, Header, Sidebar links

Tests:
- Expand backend placeholder test with dashboard assertions
- Expand discord-gateway placeholder test with config/channel assertions

AI moderation:
- llmModerationClient: improve status/reply detection, expand safety categories, fix timer reset
- userProfileLearner: fix isReply refinement
- userProfileStore: add pending cache check
- messageMetadata: add crosspost type mapping
- migrate.ts: improve partial-index safety in schema push

Co-Authored-By: Claude <noreply@anthropic.com>

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

@@ -0,0 +1,29 @@
+import { createChildLogger } from "@bete/shared/logger";
+import { dashboardRepository } from "./dashboard.repository.js";
+
+const logger = createChildLogger("dashboard.service");
+
+export interface ListUsersQuery {
+  limit: number;
+  cursor?: string;
+  search?: string;
+}
+
+export class DashboardService {
+  async getStats() {
+    logger.debug("Fetching dashboard stats");
+    return dashboardRepository.getStats();
+  }
+
+  async listUsers(query: ListUsersQuery) {
+    logger.debug({ query }, "Listing dashboard users");
+    return dashboardRepository.listUsers(query);
+  }
+
+  async getUserDetail(userId: string) {
+    logger.debug({ userId }, "Fetching user detail");
+    return dashboardRepository.getUserDetail(userId);
+  }
+}
+
+export const dashboardService = new DashboardService();