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/ARCHITECTURE.md

@@ -139,5 +139,5 @@ pipeline gauges — `ai_analysis_queued_conversations`,
   numeric snowflake IDs never trigger false positives.
 - **Semantic cache is batched** (one embed call + one Qdrant batch search),
   not N sequential round-trips. `ensureQdrantCollection` is memoized.
-- **Streaming is mandatory** against the 9router base URL (non-stream waits for
+- **Streaming is mandatory** against the omniroute base URL (non-stream waits for
   the full body and times out). `llmClient` aggregates SSE chunks.