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

package.json

@@ -8,8 +8,6 @@
     "dev:backend": "pnpm --filter './services/backend' run dev",
     "dev:discord-gateway": "pnpm --filter './services/discord-gateway' run dev",
     "dev:web": "pnpm --filter './services/frontend' run dev",
-    "build:backend": "pnpm --filter './services/backend' run build",
-    "build:discord-gateway": "pnpm --filter './services/discord-gateway' run build",
     "build:web": "pnpm --filter './services/frontend' run build",
     "typecheck": "pnpm -r run typecheck",
     "lint": "biome check --diagnostic-level=error .",