QoL: Streamline Item Pricing in Async Trade

Loving the new async trade system so far, trades go through fast and it’s been a huge improvement overall. The only thing is that trying to list a bunch of stuff takes way too many clicks when you're dealing with full tabs worth of stuff.

Right now, to move something to your shop you have to:
- Option-click the item to send it to your merchant tab.
- Set the price and then click confirm.

That’s fine for a few items, but when you’re moving over an entire stash tab it gets painful really fast. Especially when you first have to withdraw the items out from a dump tab, then re-transfer it back into your shop.

It’d be awesome if we could:
- Set a default price that auto-applies when transferring items, or
- Set a flat price per tab (like how premium tabs work), or
- Just bulk-transfer a whole premium tab to the merchant tab without having to re-click every single item.

Async trade has made buying and selling so much smoother, this would make managing listings feel a lot better and less tedious for low value items.