fix(RedactCore): reject zero address in deployConfidentialERC20

[amathxbt]

Summary

deployConfidentialERC20 is a permissionless factory function — anyone can call it. It currently checks only that the token is not WETH and has not already been deployed, but it does not check that erc20 != address(0).

Bug

function deployConfidentialERC20(IERC20 erc20) public returns (address) {
    if (address(erc20) == address(wETH)) revert InvalidWETH();
    if (_confidentialERC20Map.contains(address(erc20))) revert AlreadyDeployed();
    // ↑ No zero-address check! address(0) passes both guards.

    bytes memory initData = abi.encodeCall(ConfidentialERC20.initialize, (erc20));
    ERC1967Proxy proxy = new ERC1967Proxy(confidentialERC20Implementation, initData);
    // ConfidentialERC20.initialize does not revert for address(0) —
    // IERC20Metadata(address(0)).name() would revert, but _isFHERC20(address(0))
    // catches that and returns false, so initialize proceeds.

    _confidentialERC20Map.set(address(erc20), address(proxy));
    // ← address(0) is now permanently registered in the EnumerableMap.
    ...
}

Impact:

• The address(0) slot in _confidentialERC20Map is permanently poisoned — it cannot be removed.
• getConfidentialERC20(address(0)) returns a non-zero address, creating a potential false-positive in any code that uses zero-address as a sentinel.
• The AlreadyDeployed guard then prevents anyone from attempting to fix it with a second call.

Fix

Add if (address(erc20) == address(0)) revert InvalidERC20(); as the first check in the function.

[vercel]

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