feat: add Base network support

[mgpai22]

Summary

Add Base support to the shared UI packages and Rosen app EVM integration path.

This PR wires Base through the shared network registry, EVM helpers, Rosen app network layer, wallet exposure, explorer helpers, and icon assets.

Changes

• register Base in packages/constants and keep its chain index aligned with the shared Rosen chain list
• add Base explorer URL helpers and URL tests in packages/utils
• add a Base network icon export in packages/icons
• extend networks/evm to recognize Base and resolve BASE_RPC_API
• add Rosen app Base network wiring and expose it through MetaMask and WalletConnect
• add BASE_RPC_API to the Rosen app environment example
• add a changeset covering the affected packages

[vercel]

@mgpai22 is attempting to deploy a commit to the rosen-bridge Team on Vercel.

A member of the Team first needs to authorize it.