Payment Profile VAT Upgrades: Real-Time Validation, Auto-Normalization, Stripe Sync

Payment Profile VAT handling — multiple improvements. Real-time validation now shows status next to your VAT number as you type (verified, invalid, Romania, non-EU). VAT numbers entered with formatting (spaces, dots, dashes) or with the country prefix doubled (e.g. DE prefix + DEXXXXXX number) are auto-normalized before reaching Stripe. Tax IDs that already existed on your Stripe customer but weren't recorded on our side are now auto-detected and synced on next save in your Payment Profile — no more silent divergences between your account and Stripe. Changing the country also clears the VAT field so it can't drift into an invalid combination.