Selecting a TM in the mart's SELL pack (and the item PC's DEPOSIT pack) opened the teach-party screen: PackMenu:useSelected taught any item carrying `teaches`, even when the pack was built as a chooser (DepositSellPack, world = {}). On the cart that chooser's jumptable is four ScrollingMenus and never reaches tmhm.asm, so the row must hand back to the caller instead.
Gate the teach and field-NOUSE branches behind world.useFieldItem so only the real field PACK teaches; choosers now hand TMs to onChoose. Selling then prices a TM at half its ItemAttributes price -- exactly half of what the Goldenrod/Celadon TM shelves charge, and half of the hidden price for the rest, the way SelectQuantityToSell -> GetItemPrice -> Sell_HalvePrice does on the cart.
Closes#1243
ShaneMcGovernIE
bryanthaboi