chore: migrate AI LLM router from 9router to omniroute

Switch GMW's AI LLM base URL from 9router (https://9router.asepharyana.my.id/v1)
to omniroute on imrnes (http://100.121.180.82:20128/api/v1).

- Update default AI_LLM_BASE_URL in discord-gateway + backend config schemas
- Update .env.example documentation
- Update all 9router references in comments/docs/tests to omniroute
- Production BWS secret gmw_ai_llm_base_url already updated

Omniroute uses /api/v1 prefix (not /v1 like 9router), so the base URL
now correctly points at the right API path for the OpenAI SDK.

services/discord-gateway/tests/visionNoImageSeen.test.ts

@@ -6,7 +6,7 @@
 // a VALID vision_llm result. Every later analysis of the same image (same
 // hash / phash) then hit the poisoned cache and the moderation LLM wrote
 // "lampiran yang gagal terbaca" — image analysis seemed permanently broken
-// even though 9router was responding fine.
+// even though omniroute was responding fine.
 import { describe, expect, it } from "vitest";
 import { isNoImageSeenText } from "../src/modules/ai-moderation/visionAnalyzer.js";