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.routes.ts

@@ -0,0 +1,52 @@
+import { createChildLogger } from "@bete/shared/logger";
+import type { Request, Response, Router } from "express";
+import express from "express";
+import { asyncHandler } from "../../shared/middlewares/index.js";
+import { dashboardService } from "./dashboard.service.js";
+
+const logger = createChildLogger("dashboard.routes");
+
+export function createDashboardRouter(): Router {
+  const router = express.Router();
+
+  // GET /api/dashboard/stats — aggregated server statistics
+  router.get(
+    "/dashboard/stats",
+    asyncHandler(async (_req: Request, res: Response) => {
+      logger.debug("Fetching dashboard stats");
+      const stats = await dashboardService.getStats();
+      res.json(stats);
+    }),
+  );
+
+  // GET /api/dashboard/users — paginated user list with profiles
+  router.get(
+    "/dashboard/users",
+    asyncHandler(async (req: Request, res: Response) => {
+      const limit = Number(req.query.limit) || 20;
+      const cursor =
+        typeof req.query.cursor === "string" ? req.query.cursor : undefined;
+      const search =
+        typeof req.query.search === "string" ? req.query.search : undefined;
+
+      const result = await dashboardService.listUsers({
+        limit,
+        cursor,
+        search,
+      });
+      res.json(result);
+    }),
+  );
+
+  // GET /api/dashboard/users/:userId — single user detail
+  router.get(
+    "/dashboard/users/:userId",
+    asyncHandler(async (req: Request, res: Response) => {
+      const userId = String(req.params.userId);
+      const detail = await dashboardService.getUserDetail(userId);
+      res.json(detail);
+    }),
+  );
+
+  return router;
+}