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/discord-gateway/drizzle/migrations/0012_light_prism.sql

@@ -0,0 +1 @@
+CREATE INDEX IF NOT EXISTS "idx_messages_guild_ai_status_analyzed" ON "messages" USING btree ("guild_id","ai_status","ai_analyzed_at","id");--> statement-breakpoint

services/discord-gateway/drizzle/migrations/meta/_journal.json

@@ -85,6 +85,13 @@
       "when": 1781388000000,
       "tag": "0011_add_voice_transcription",
       "breakpoints": true
+    },
+    {
+      "idx": 12,
+      "version": "7",
+      "when": 1781672400000,
+      "tag": "0012_light_prism",
+      "breakpoints": true
     }
   ]
 }