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

packages/shared/src/database/schema.ts

@@ -95,6 +95,9 @@ export const pgMessagesTable = pgTable(
     threadAiStatusCreatedIdx: pgIndex(
       "idx_messages_thread_ai_status_created",
     ).on(table.thread_id, table.ai_status, table.created_at, table.id),
+    guildAiStatusAnalyzedIdx: pgIndex(
+      "idx_messages_guild_ai_status_analyzed",
+    ).on(table.guild_id, table.ai_status, table.ai_analyzed_at, table.id),
   }),
 );