Manabox list exports (and potentially CSV too) have incompatible set codes for Token cards

When importing card lists from Manabox, tokens are exported with a "T" prefix in their set codes (e.g., "TMTG" instead of "MTG"). Currently, CardNexus throws an error for these unrecognized set codes, requiring users to manually remove the "T" prefix. Since different platforms handle token set codes differently - some include tokens in the parent expansion while others use the T-prefix convention - it would be helpful if CardNexus could automatically handle both formats. A simple solution would be to check if a 4-character set code starting with "T" isn't recognized, then retry with the first character removed to map it to the parent expansion.