fix(validation): blockHeightField uses || instead of ?? causing silent max-height fallback when currentBlockHeight is 0

blockHeightField
uses || instead of ??, allowing invalid block heights when current height is 0

The
blockHeightField
validator in
src/lib/formValidation.ts
(lines 123–124) uses the || (OR) operator to determine the max allowed block height. Since 0 is falsy in JavaScript, when currentBlockHeight === 0 (e.g. regtest before any blocks are mined), the max silently becomes Number.MAX_SAFE_INTEGER instead of 0 — meaning any block height passes validation when it should be rejected

const maxBlockheight = Math.max(minBlockHeight, currentBlockHeight || INPUT_BLOCK_HEIGHT_MAX)