Selecting an NFT as a user's PFP should verify ownership

**Current Behavior**
Any user can choose any NFT to be their pfp.

**Expected Behavior**
The frontend should verify that the user owns the PFP they are claiming is theirs.
This can be checked on read only, i.e. when a user's pfp is loaded, if they do not own the nft they claim to own, then there should be a warning symbol next to their image.
To do this, the current structure will have to change so that the backend stores the contract address and token id of the NFT the user claims to own.
The frontend then checks the contract for that information, loads the pfp, and shows a warning sign next to the image if the user no longer owns it.

Start by tracing the existing frontend PFP selection and loading flow alongside the backend user-profile storage described in the issue. Confirm where the NFT contract address and token ID can be stored and where ownership can be checked; done means an owned NFT loads normally and a no-longer-owned NFT displays a warning symbol.

Written by the indexing model from the issue text.