chore: post-deployment cleanup and docs update

- Make AI routing rules DB-driven (read from system_configs, removed from config.py)
- Add translation quota tracking to LLM translation (OpenAIProvider)
- Add Alibaba MT ECS RAM role support (STS token, no AccessKey needed)
- Fix admin sidebar link for AI模型配置 page
- Fix Quota.vue API path (quotas → translation-quotas)
- Fix login auto-redirect to dashboard
- Add provider dropdown selects to AI routing config UI
- Clean up stale ai_provider_* system_configs records
- Remove OpencodeGo, Spark providers (code + DB)
- Update deploy config: nginx port 8000, systemd cwd

backend/app/api/v1/admin_ai.py

@@ -42,9 +42,7 @@ class AIProviderUpdate(BaseModel):
 
 PROVIDER_TYPE_LABELS = {
     "sensenova": "Sensenova (商汤)",
-    "opencode_go": "OpencodeGo",
     "nvidia": "NVIDIA",
-    "spark": "讯飞 Spark",
     "alibaba-mt": "阿里翻译",
 }