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

.env.example

@@ -40,7 +40,10 @@ NODE_ENV=development                    # Environment: development|production|te
 VERBOSE=false                           # Enable verbose/debug logging (default: false)
 
 # === Admin ===
-ADMIN_PASSWORD=admin123                 # Backend admin password for API auth (default: admin123)
+# ADMIN_PASSWORD=***              # REQUIRED — Backend admin password for dashboard auth
+                                     # WARNING: No default! If not set, the server won't start.
+DASHBOARD_IS_PUBLIC=false            # Allow dashboard access without auth? (default: false)
+                                     # When true, GET requests are public; mutations still need auth.
 
 # === Database (PostgreSQL) ===
 # Option 1: Connection string (overrides individual params)