Feat/wallet provider abstraction

[nursetechie]

Description

• Created the generic IWalletProvider mock adapter in src/providers/embedded-wallet.provider.js.
• Implemented createWallet and getWallet methods that explicitly return only public addresses, completely protecting backend from private keys.
• Wired the new provider into the DI container in src/app.js.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Testing

Closes #51
closes #51

Checklist

• Code follows style guidelines (npm run lint run)
• Tests added/updated and npm run test passes
• Documentation updated