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/message-capture/messageMetadata.ts

@@ -237,7 +237,8 @@ export function getMessageMetadata(message: Message): RichMessageMetadata {
           messageId: message.reference.messageId ?? null,
           channelId: message.reference.channelId ?? null,
           guildId: message.reference.guildId ?? null,
-          type: (message.reference.type as unknown as string | undefined) ?? null,
+          type:
+            (message.reference.type as unknown as string | undefined) ?? null,
         }
       : null,
     isCrosspost: message.flags?.has(1 << 1) ?? false,