Add support for browser wallet providers (Freighter/Albedo) in Client

[Code-Paragon]

Problem

The YieldStreamClient currently only supports raw Keypair instances for signing, lacking the TODO implementation for browser-based wallet providers like Freighter.

Expected behavior

The constructor and configuration interfaces are expanded to accept an abstract wallet provider or signer callback, allowing the frontend dashboard to delegate signing without exposing raw private keys.

Files to update

• src/client.ts
• src/modules/vault.ts

Project relevance

This is critical for integrating the SDK seamlessly into the Next.js yieldstream-dashboard where non-custodial wallet extensions are the primary interaction method.

Acceptance criteria

• Feature works as described
• Tests are added or updated where needed
• Documentation is updated where needed
• YieldStreamConfig accepts an optional walletProvider interface
• No TypeScript, lint, test, or build errors