Public — active plans for an app, dynamic from Stripe

Plan titles/prices/descriptions/features straight from Stripe (no hardcoding). Public — pricing is public (a pricing page renders before sign-in). Free + Enterprise (no Stripe price) are added by the frontend as bookends.

A BRANDED host prices exactly one brand: its own, resolved from an authoritative signal (ALGENTA_PRODUCT, else the request's own Host via the registry's public_api_base). A request for a DIFFERENT brand on a branded host is refused rather than served: cross-brand pricing stays possible only on the shared engine's own non-brand host, which is where a multi-brand portal belongs. ?app=<own brand> remains valid so existing callers keep working.

An unregistered app is rejected with an error rather than an empty plan list under a 200, so the response distinguishes "this brand has no paid tiers" from "no such brand".