- Renamed "Public URL / Prefix" to "Public Access URL" in Profile Modal to differentiate from S3 API Endpoint.
- Added helper text clarifying that Account ID is used for connection and Public URL is for CDN.
- Implemented validation in `ProfileModalController` to detect and warn if an S3/R2 API endpoint is entered into the Public URL field.
- Added blocking validation on save to prevent misconfiguration.
- Verified changes with unit tests and Playwright frontend verification.