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/src/views/WorkspaceLanding.vue

@@ -193,7 +193,8 @@ async function register() {
     regForm.password = ''
   } catch (e) {
     const map = { 'Phone already registered': '该手机号已被注册', 'Invalid credentials': '手机号或密码错误' }
-    regError.value = map[e?.detail] || e?.detail || '注册失败'
+    const detail = typeof e === 'string' ? e : e?.detail
+    regError.value = map[detail] || detail || '注册失败，请检查网络连接'
   } finally {
     regLoading.value = false
   }