Integrate Stellar SDK and Wallet Connection

[SimpleX-T]

Priority: High

Description: Integrate the Stellar .NET SDK to enable blockchain connectivity and wallet management for the BookamApi platform.

Acceptance Criteria:

• Add Stellar .NET SDK (stellar-dotnet-sdk) as a dependency
• Create StellarService for blockchain interactions
• Implement wallet generation for new users
• Add support for connecting existing Stellar wallets (Freighter, Albedo, xBull)
• Create endpoints for wallet connection and verification
• Implement Stellar testnet and mainnet configuration options

Technical Details:

// Services/IStellarService.cs
public interface IStellarService
{
    Task<KeyPair> GenerateWalletAsync();
    Task<bool> VerifyWalletOwnershipAsync(string publicKey, string signature);
    Task<AccountResponse> GetAccountBalanceAsync(string publicKey);
    Task<bool> FundTestnetAccountAsync(string publicKey);
}

Stellar Ecosystem Value:

• Onboards users to Stellar ecosystem through seamless wallet integration
• Enables secure, decentralized identity management
• Foundation for all future Web3 features