Set Photographer Lock Endpoint

Lock or unlock ONE photographer across several projects in a single call.

The All-Projects photographers table needs this: a photographer spans many projects, and doing it with the per-project full-list replace would mean N read-modify-write round trips racing each other. This touches only the one photographer's rows, so concurrent edits to other photographers in the same project can't clobber each other either.

Authorised per project — the caller's projects are filtered to those where they actually hold settings.manage.lockedPhotographers, so an All-Projects click can't reach a project they don't administer. Returns the projects actually changed.