## Problem
In the default deployment (`API_PROXY_SCHEME=python`), the nginx config
generated from `docker/nginx/ragflow.conf.python` uses:
```nginx
proxy_pass http://localhost:9381; # admin
proxy_pass http://localhost:9380; # api
```
Inside the RAGFlow container, `/etc/hosts` maps `localhost` to both
`127.0.0.1` and `::1`:
```
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
```
But the backend services (`ragflow_server.py` on 9380, admin server on
9381) only listen on IPv4 (`127.0.0.1`). When nginx resolves `localhost`
to `::1`, the upstream connection fails and nginx falls back to the IPv4
address - each fallback adds ~1 second of latency.
Co-authored-by: Jin Hai <haijin.chn@gmail.com>
### What problem does this PR solve?
1. Refactor go server log
2. Update docker building, since nginx config should be set according to
the deployment.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
---------
Signed-off-by: Jin Hai <haijin.chn@gmail.com>
