Introduce a Pennant PriceExperiment feature (control vs a higher price tier),
salted independently of the trial experiment. The assigned variant's prices and
Stripe lookup keys flow through ExperimentOffer into the shared pricing prop
(paywall + upgrade dialogs) and into checkout server-side, so the price shown
always equals the price charged. stripe:sync-prices now also creates the variant
tiers. Inert until PRICE_EXPERIMENT_STARTED_AT is set.
Víctor Falcón