Return the v2 field catalog + presets so the frontend can build its picker.

Stays usable unauthenticated (it is just a catalog), but when a caller does present credentials we also return the fields THEIR plan is entitled to. The picker needs that to default to "everything I can actually get" rather than pre-ticking fields the backend will silently drop — which is how the Starter plan ended up advertising hours it could never deliver.

Entitlement is resolved through plan_benefits, the same admin-editable table clamp_fields_to_plan() uses, so the picker cannot drift from enforcement.