- UpstreamClient & Sub2ApiWebsiteClient: add __enter__/__exit__
- Convert all call sites to `with Client(...) as c:` pattern
- Remove unused `upstream_name`/`upstream_base_url` locals in scheduler
- Fix stale _decimal_str→decimal_string in _rate_from_group
Enable managed remote browser custom pages with login autofill and add website sync workflows so external admin surfaces can be handled inside SmartUp.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>