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

admin-frontend/src/router/index.js

@@ -2,7 +2,7 @@ import { createRouter, createWebHistory } from 'vue-router'
 import AdminLayout from '@/layouts/AdminLayout.vue'
 
 const routes = [
-  { path: '/login', redirect: '/' },
+  { path: '/login', redirect: to => ({ path: '/', query: to.query }) },
   { path: '/', name: 'Landing', component: () => import('@/views/Landing.vue') },
   {
     path: '/dashboard',