Add support for the Sepolia testnet alongside Ethereum mainnet:
- New src/shared/networks.js with network definitions (mainnet + sepolia)
including chain IDs, default RPC/Blockscout endpoints, and explorer URLs
- State now tracks networkId; defaults to mainnet for backward compatibility
- Network selector in Settings lets users switch between mainnet and Sepolia
- Switching networks updates RPC URL, Blockscout URL, and chain ID
- All hardcoded etherscan.io URLs replaced with dynamic explorer links
from the current network config (sepolia.etherscan.io for Sepolia)
- Background handles wallet_switchEthereumChain for both supported chains
and broadcasts chainChanged events to connected dApps
- Inpage provider fetches chain ID on init and updates dynamically via
chainChanged events (no more hardcoded 0x1)
- Blockscout API uses eth-sepolia.blockscout.com for Sepolia
- Etherscan label/phishing checks use the correct explorer per network
- Price fetching skipped on testnets (tokens have no real value)
- RPC validation checks against the selected network's chain ID
- getProvider() uses the correct ethers Network for Sepolia
API endpoints verified:
- Etherscan: sepolia.etherscan.io
- Blockscout: eth-sepolia.blockscout.com/api/v2
- RPC: ethereum-sepolia-rpc.publicnode.com
closes#110
