refactor(server): use env var for wallet password and improve setup

[gitsrc]

This commit refactors the wallet management in the DANP-MCP-SERVER.

Key changes:

• Replaces the hardcoded wallet password with the 'WALLET_PASSWORD' environment variable to enhance security.
• Extracts wallet initialization into a dedicated 'setupWallet' function to improve code organization and modularity.
• Adds detailed logging to the wallet setup process, including printing the active wallet address for better operational visibility.
• Updates the .gitignore file to exclude all '.env' files and the local 'wallet.json' from version control, preventing accidental credential leaks."