Derive Stripe test/live mode from the API key prefix at boot, failing on
unrecognized prefixes, and drop the separate `stripe-mode` config key.
Refine disabled controls to render through the shared `disabledControl`
part with the not-allowed cursor, and add a lint rule refusing
hand-rolled disabled buttons.
Adjust plan cards to offer no purchase control on free rungs, fix bound
checkbox Bool handling, and rename "Public/Private" to "Listed/Unlisted"
with enhanced readiness verdicts.