Editable OUSD Input

We've been discussing in various places whether or not both sides of the swap form should have editable dropdowns for the currency selection (notice that OUSD is fixed). The initial arguments for it were that (1) Uniswap allows the user to change the currency on either side of the equation and (2) it's not obvious that the arrow should be clicked to flip the elements. We addressed the latter by making OUSD one of the options for the input so that the user could cause them to flip by changing the top one (or clicking the arrow). The argument against making both editable was that the current version effectively communicates that OUSD must be involved in the swap. We don't currently support swapping USDC for USDT in our DApp. I guess there's no reason why we can't do that, it just seems like unnecessary engineering work without much benefit. There's not really any reason for users to come to our DApp for swaps that don't involve our contracts. They might as well just go to Uniswap's DApp because our contracts require OUSD to be involved by design.

I subsequently realized that it's a little frustrating for the DApp to be presumptuous about what the user wants when the selections aren't applicable after the flip. Making both sides editable would go hand-in-hand with supporting empty selections.

I could go either way on this but wanted to document it for us to revisit.

No files or tests are identified. Start by locating the swap form and reviewing the existing currency-selection behavior alongside the linked Loom recording. Before implementation, settle whether both sides should be editable and whether empty selections are supported; the issue has no concrete acceptance criteria.