42. Multi-chain abstraction

A multi-chain wallet needs an abstraction over chain-specific details (RPC endpoints, gas token, address format, block explorer URL) so screens don't hardcode assumptions about a single network.

interface ChainConfig {
  id: number;
  name: string;
  rpcUrl: string;
  nativeSymbol: string;
  explorerUrl: string;
}

const CHAINS: Record<number, ChainConfig> = {
  1: { id: 1, name: "Ethereum", rpcUrl: "https://eth.llamarpc.com", nativeSymbol: "ETH", explorerUrl: "https://etherscan.io" },
  8453: { id: 8453, name: "Base", rpcUrl: "https://mainnet.base.org", nativeSymbol: "ETH", explorerUrl: "https://basescan.org" },
};

function txUrl(chainId: number, hash: string) {
  return `${CHAINS[chainId].explorerUrl}/tx/${hash}`;
}

Keeping chain config data-driven (rather than scattered `if (chainId === 1)` checks) makes adding a new supported chain a config change, not a re-architecture.

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