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/src/modules/ai-moderation/stickerPrompt.ts

@@ -67,6 +67,24 @@ export function buildStickerTextOnlyWarning(
   );
 }
 
+/**
+ * Build a neutral fallback text when an image/video attachment cannot be
+ * downloaded or analyzed. Unlike the sticker warning, this is deliberately
+ * neutral — it only records *that* an attachment existed, without any
+ * instruction to the LLM about how to treat it. The absence of visual
+ * data already means the LLM must rely on message content alone.
+ *
+ * Returns a formatted string for inclusion in the media context block.
+ */
+export function buildAttachmentTextOnlyWarning(
+  filename: string,
+  messageId: string,
+): string {
+  const fallback = `[attachment: "${filename}" dari pesan id=${messageId} — tidak tersedia untuk analisis visual]`;
+  logger.debug({ filename, messageId }, "Built attachment text-only fallback");
+  return fallback;
+}
+
 /**
  * Prompt used when a custom emoji image was successfully downloaded
  * and is being sent to the vision LLM as a base64 image.