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

user-frontend/vite.config.js

@@ -15,7 +15,7 @@ export default defineConfig({
   server: {
     port: 5174,
     proxy: {
-      '/api': { target: 'http://localhost:8002', changeOrigin: true }
+      '/api': { target: 'http://localhost:8000', changeOrigin: true }
     }
   }
 })