fix: deepseek-reasoner test failure and missing nginx /api proxy

[qirobot]

Summary

Two independent fixes hit while bringing up the project via docker compose:

1. deepseek-reasoner 模型测试始终报 "API响应为空"

In app/services/config_service.py::_test_deepseek_api:

• max_tokens was 50. deepseek-reasoner first emits reasoning_content (思考过程) before the final content. With only 50 tokens the model is still mid-reasoning, so choices[0].message.content comes back empty and the test reports "API响应为空".
• timeout was 10s, which is also too tight for reasoner — it routinely thinks for 30–90s.

Bumped to max_tokens=2000 and timeout=120. deepseek-chat is unaffected (small response, well under the new cap).

2. Docker 前端登录 405 (Method Not Allowed)

docker/nginx.conf has no /api/ rule, so the SPA's POST /api/auth/login falls through to the static-file location / block. nginx then refuses POST on a static route → 405. Login is impossible until this is fixed.

Added a standard reverse-proxy block:

location /api/ {
    proxy_pass http://backend:8000;
    proxy_http_version 1.1;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_read_timeout 300s;
    proxy_connect_timeout 60s;
    proxy_send_timeout 300s;
}

The backend hostname matches the service name in docker-compose.yml, so it works out of the box for fresh docker compose up users.

Test plan

• deepseek-chat 测试仍然通过（回归）
• deepseek-reasoner 测试通过（之前必失败）
• 前端 admin / admin123 登录成功（之前 405）
• 普通后端 API 调用经 nginx 反代正常返回