fix(nextjs): parse the unshield amount in confidential decimals

[Dusk1e]

The unshield amount is parsed with the wrong decimals. useUpdateEncryptDecryptValue always does parseUnits(sanitized, pair.publicToken.decimals), but in the decrypt direction that value goes straight into unshield(from, to, uint64 amount), which takes the amount in the confidential token's own decimals, and the FHERC20 wrapper caps those at 6. The call site in MainTokenSwapping already passes tokenDecimals: pair.confidentialToken.decimals for that same value, so only the parse disagreed.

For the ETH pair (public 18, confidential 6) typing 1 gives 1e18 where the contract wants 1e6. You mostly can't get that far though, because useEncryptDecryptValueError compares the input against the decrypted confidential balance, which is in 6 decimals. Holding 1 eETH that comparison is 1000000000000000000 against 1000000, so anything you type comes back as insufficient balance. The percent buttons show the same split from the other end: they already store the right raw value, but useEncryptDecryptInputValue renders it with public decimals, so 50% of 1 eETH appears in the box as 0.0000000000005 instead of 0.5.

useUpdateEncryptDecryptValueByPercent was already choosing decimals by direction, so I lifted that expression into a small inputDecimals(pair, isEncrypt) helper and used it in all three places. Shield is untouched, shield(to, uint256 amount) really does take underlying units and that call site already passes publicToken.decimals.

Worth noting why this went unseen: the token list only ships USDC and EURC, both 6 decimals, so public and confidential coincide and nothing looks wrong. ETH is the pair that breaks and it has its own branch in the selector.

There is no test runner in packages/nextjs, so I could not add a test. check-types passes, lint reports no errors (the prettier warnings it prints are pre-existing, all in the generated lib/abis.ts), and prettier --check passes on the changed file.

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