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/http/app.ts

@@ -9,7 +9,7 @@ import helmet from "helmet";
 import { createAnalysisRouter } from "../modules/analysis/analysis.routes.js";
 import { createAuthRouter } from "../modules/auth/auth.routes.js";
 import { createConfigRouter } from "../modules/config/config.routes.js";
-import { createCorrectionsRouter } from "../modules/corrections/corrections.routes.js";
+import { createDashboardRouter } from "../modules/dashboard/dashboard.routes.js";
 import { createHealthRouter } from "../modules/health/health.routes.js";
 import { createMascotChatRouter } from "../modules/mascot-chat/mascot-chat.routes.js";
 import { createMediaRouter } from "../modules/media/media.routes.js";
@@ -64,7 +64,7 @@ export function createHttpApp(): Express {
   // API routes
   app.use("/api", createAuthRouter());
   app.use("/api", createConfigRouter());
-  app.use("/api", createCorrectionsRouter());
+  app.use("/api", createDashboardRouter());
   app.use("/api", createMessagesRouter());
   app.use("/api", createAnalysisRouter());
   app.use("/api", createMascotChatRouter());