⌨️ New zero-dependency CLI

```bash
npx @didrod2539/checkdigit validate 4111111111111111 # ✓ valid credit-card (Visa)
echo "DE89 3704 0044 0532 0130 00" | npx @didrod2539/checkdigit validate
npx @didrod2539/checkdigit generate card --brand Amex # a format-valid TEST card
```

• `validate ` auto-detects card / IBAN / ISBN / barcode and exits non-zero when the check digit is wrong.
• `generate <card|isbn|barcode|luhn>` makes format-valid test data (correct checksum, not a real account).

Still zero dependencies.

💖 Sponsor via Lemon Squeezy.

First public release of checkdigit — validate & generate checksummed IDs, locally.

• luhn (mod-10), creditCard (brand/validate/format/generateTest), iban (mod-97-10), isbn (10/13 + convert), barcode (EAN-13/EAN-8/UPC-A)
• detect() + validate() auto-detect the identifier type
• Exact check-digit math, zero dependencies, ESM + CJS + types
• Free local-only web app: https://didrod205.github.io/checkdigit/

npm install checkdigit