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/frontend/src/App.tsx

@@ -1,10 +1,10 @@
 import { useEffect, useMemo, useState } from "react";
 import { AuthOverlay } from "./features/auth";
+import { DashboardPanel } from "./features/dashboard";
 import { LivePanel } from "./features/live";
 import { useMediaControl } from "./features/live/hooks/useMediaControl";
 import { useVoiceControl } from "./features/live/hooks/useVoiceControl";
 import { MessagesPanel } from "./features/messages";
-import { TunerPanel } from "./features/tuner";
 import { ModerationAlertListener } from "./features/messages/components/ModerationAlertListener";
 import {
   mergeMessages,
@@ -183,11 +183,11 @@ export default function App() {
             onVolumeChange={media.setVolume}
           />
         )
-      ) : activeTab === "tuner" ? (
+      ) : activeTab === "dashboard" ? (
         !isAuthenticated ? (
           <AuthOverlay onAuthenticated={() => setIsAuthenticated(true)} />
         ) : (
-          <TunerPanel />
+          <DashboardPanel />
         )
       ) : (
         <MessagesPanel