Fixed: a fresh install no longer gets stuck on an error screen

On a fresh install, Subi's admin needs to exchange a session token with Shopify before it can load. That token normally comes from Shopify's App Bridge, but when App Bridge failed to return one, the app had no fallback: it dead-ended on an error screen instead of completing the install.

This has happened on at least 42 shops since early September, including one case where the error lasted roughly 37 minutes before the merchant could get in. The app now falls back to a token it already captured from the install URL when App Bridge comes back empty, and completes the same token exchange with it instead of stopping.

This only affects the moment of installing the app for the first time; merchants who already have Subi installed and running are not affected.