Typing SOULSYNC_WEB_BIND_HOST=0.0.0.0 every launch is awkward. `python dev.py --lan`
sets it for you (binds 0.0.0.0 so other devices can reach it); plain `python dev.py`
stays localhost-only. Set before build_backend_env() so it propagates to both the
direct (Windows) and gunicorn backend modes.
- Adopt Base UI for the shared form field, input, button, and toggle wrappers
- Replace the local class-name helper with clsx to keep the primitives simpler
- Keep native textarea and select controls where they still fit the existing styling pattern
- Replace the shell convenience script with a cross-platform Python launcher.
- Keep dev.sh as a Unix compatibility wrapper.
- Let the direct backend bind with host and port overrides.
- Update the root and webui README guidance for the new launcher.
- Preserve the backend startup behavior used by the old dev flow.