bug: hardhat.config.ts uses evmVersion: "prague" — confirm Arc Testnet supports Prague opcodes or update to supported target

[osr21]

Summary

The hardhat.config.ts in this repository specifies:

solidity: {
  version: '0.8.29',
  settings: {
    optimizer: { enabled: true, runs: 200 },
    evmVersion: 'prague',
  },
},

prague is the EVM target for EIP-7702 (account
abstraction via AUTH/AUTHCALL opcodes). Developers who copy this configuration to deploy
their own contracts may encounter one of two problems:

1. Silent bytecode incompatibility — if Arc does not implement all Prague opcodes, contracts
   compiled with evmVersion: 'prague' may deploy successfully but fail at runtime when a
   Prague-specific opcode is executed.

2. ArcScan verification failure — Blockscout requires the EVM version to match the deployed
   bytecode exactly. If a developer uses the repo's prague setting for compilation but
   Blockscout doesn't recognise prague as a valid option, verification fails with no clear
   error message.

Reproduction

# Check which EVM version hardhat.config.ts uses:
grep evmVersion hardhat.config.ts
# → evmVersion: 'prague'

From our DApp development experience, contracts compiled with evmVersion: 'shanghai' and
evmVersion: 'paris' both deploy and verify successfully on Arc Testnet. We have not
confirmed whether prague-compiled bytecode runs correctly on Arc Testnet.

Suggested fix

1. Confirm which EVM version Arc Testnet currently supports
2. If Arc does not yet support Prague opcodes, change the default evmVersion in
   hardhat.config.ts to the highest supported version (likely shanghai)
3. Document the supported EVM version in the developer docs

Impact

Any developer who clones this repo, uses the hardhat.config.ts as a starting point for their
own contracts, and then deploys to Arc Testnet may see hard-to-diagnose failures. The config file
is the authoritative reference developers use when getting started.

Environment: Arc Testnet (chainId 5042002), Hardhat 2.x, @nomicfoundation/hardhat-toolbox-viem