feat: Complete Wallet Recovery Implementation.

# Problem
Currently, the BDK Demo app lacks a way for testers to view their wallet's recovery information once the wallet is created. Specifically, there is no UI to access the Descriptors (External and Internal) or the Mnemonic Phrase. This is important for testing purposes.

## Question
This is a wallet-specific setting, so is the placeholder settings route meant for a global or wallet-specific settings?

## Suggestion
If its meant for a global settings i suggest we create a wallet specific section to view the Phrase because putting it in a global settings might make it harder to associate with a specific active wallet.

Start by inspecting the placeholder settings route and resolve whether settings are global or wallet-specific. Done means the active wallet has a UI for viewing both external and internal descriptors and its mnemonic phrase, with the wallet association clear.

Written by the indexing model from the issue text.