Add _normalize_uid static method to FusionClockNfcKiosk that strips
whitespace, uppercases, removes separators, validates hex-only content,
and reformats to canonical colon-separated pairs; returns None for
empty/invalid input. Covered by 7 new TransactionCase unit tests.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>