Network Selector

<img width="644" height="489" alt="Image" src="https://github.com/user-attachments/assets/17bc9cca-0d70-4dc7-982f-52108642bbc6" />

Hi team, I use this from time to time and feel like auto-suggesting API routes while changing from mainnet and testnet would help save time. People can still be allowed to enter their own URL but we assume they generally use the provided ones.