feat: migrate frontend to Astro + expand AI moderation + backend admin/runtime config

Frontend:
- migrate from Vite to Astro (astro.config.mjs, pages/, layouts/)
- add admin panel, settings page, command palette, error boundary
- refactor App.tsx, MascotChatbot, Sidebar, Header, DashboardLayout
- update API client, WebSocket, auth, dashboard features

Backend:
- add admin module and config routes
- refactor middlewares, Redis connection, WebSocket server/bridge
- add runtime config loader

Discord Gateway:
- refactor AI moderation: circuit breaker, concurrency limiter, fallback processor
- add media analysis client, Seaxng search, user profile learner
- add new drizzle migration

Shared:
- extend database schema, add new config fields

services/backend/src/modules/dashboard/dashboard.service.ts

@@ -29,6 +29,7 @@ export class DashboardService {
     limit: number;
     search?: string;
     guildId?: string;
+    cursor?: string;
   }) {
     logger.debug({ query }, "Listing dashboard channels");
     return dashboardRepository.listChannels(query);