MinterHandlerV2 uncollateralized self-mint

Summary

mint()'s zero-amount guard and 2%-band collateral/usnAmount ratio check are both gated behind order.user != msg.sender, so any address holding MINTER_ROLE that is also a whitelisted user can self-mint an arbitrary usnAmount with collateralAmount = 0.

Root cause

Falsifies the invariant 'USN minted via MinterHandlerV2.mint() is always backed by proportional collateral' - both safety checks are skipped entirely for the self-mint case.

Verification

Confirmed live, not hypothetical: the address holding MINTER_ROLE, DEFAULT_ADMIN_ROLE, and whitelistedUsers simultaneously on the real, currently-active MinterHandlerV2 was identified on-chain. Passing mainnet-fork Foundry test using a fresh test-controlled EOA granted the identical real role.

Verified against real, live deployed contract state.