webtools' nginx now reverse-proxies /admin/ to the webadmin container
(docker/conf/webtools-nginx.conf), which no longer publishes its own
port -- everything is reachable through port 80 alongside the GM
toolbox. Added a link to it in webtools/index.html's sidebar.
Flask needs to know it's mounted under /admin/ to generate correct
url_for()/redirect() targets, so app.py now wraps the app in
werkzeug's ProxyFix (x_prefix/x_proto/x_for/x_host) reading the
X-Forwarded-Prefix header nginx sets; verified redirects, form
actions, and links all come back /admin/-prefixed end to end through
port 80.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
