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/backend/src/shared/config/index.ts

@@ -131,7 +131,7 @@ export const configSchema = z
     AI_LLM_BASE_URL: z
       .string()
       .url()
-      .default("https://9router.asepharyana.my.id/v1"),
+      .default("http://100.121.180.82:20128/api/v1"),
     AI_LLM_MODEL: z.string().default("text"),
     AI_LLM_VISION_MODEL: z.string().optional(),
     AI_LLM_EMBEDDING_MODEL: z.string().optional(),