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/discord-gateway/src/modules/ai-moderation/userProfileLearner.ts

@@ -6,8 +6,8 @@ import {
   messagesTable,
   userProfilesTable,
 } from "../../shared/database/schema.js";
-import { updateUserProfile } from "./userProfileStore.js";
 import { llmChat } from "./llmClient.js";
+import { updateUserProfile } from "./userProfileStore.js";
 
 const PROFILE_LEARNING_INTERVAL = 1000 * 60 * 60 * 12; // 12 hours
 const log = createChildLogger("userProfileLearner");