Expose styles.css via package exports so Next.js can import snappycart/styles.css

[idncod]

Problem:
Next.js App Router users can’t import Snappycart styles using import "snappycart/dist/styles.css" or import "snappycart/styles.css" because the CSS file isn’t exposed as an importable subpath. Next fails with:

Module not found: Can't resolve 'snappycart/dist/styles.css'

Acceptance criteria:

• snappycart/styles.css is a valid import path in Next.js (Turbopack and Webpack).

• Package exports include the CSS entry.

• README includes a short “Styles” section showing the correct import.

• Release a patch version.