Copilot web content control moves into Settings

Copilot adoption gets messy when users cannot tell whether an answer came from work data, the public web, or both. The old Work/Web split already confused many teams, especially where admins allowed web grounding but users did not understand the consequence. Moving the preference into Settings gives users a more persistent place to control web content where policy allows it. It also gives adoption leads a simple setup check to add to first-run training instead of relying on people to notice the grounding mode in the moment.