Add optional YAMA_WEB_BASE_PATH to mount the whole web UI (index, manifest,
static assets, /health, /api/devices, /ws) under a URL prefix such as
/remoter behind a reverse proxy. index.html now uses a __BASE_PATH__
placeholder substituted at serve time, the PWA manifest start_url is rooted
at the base path, and a mount wrapper redirects the bare prefix to prefix/
and strips it before routing. Include nginx, systemd, and env-file deployment
examples for the subpath setup.
The shared placeholder is also handled by the MFC server, which serves from
the domain root and strips __BASE_PATH__ (to "") so its web remote desktop
URLs stay rooted.
Co-Authored-By: deepseek-v4-pro
