Support sending valid transactions directly to opencbdc-tx

[HalosGhost]

Right now, this wallet operates as a standalone proof-of-concept, but the backing node-js module is capable of talking to sentinels.

So, practically, the only thing necessary for this standalone proof-of-concept to interact directly with a live-running copy of opencbdc-tx is the ability to send minting transactions (or, alternatively, importing keys/inputs). (Note: this is only necessary because right now this PoC doesn't include any method of getting funds into the UHS or importing funds which are in the UHS into the wallet; once either functionality is available, valid transfer transactions can be generated and sent to a live-running sentinel.)

A simple way of implementing this would be to add a new page meant for administrative operations allowing you to send a mint transaction to -tx for a given secret key. This would replace the fund button in the wallet page. That same page could instead allow importing an input (as exported by the opencbdc-tx client). Once done, a few configurations can be changed to forward transfer transactions to the actual transaction processor rather than a mock process.

• Note also that any PR addressing this issue should also update the README's opening paragraphs.