feat: add Razorpay/dodo adapter and provider-agnostic payments interface

The npx next-forge init flow unconditionally scaffolds Stripe. Stripe isn't available in India, and several other regions (parts of SEA, LATAM) have the same issue. Users hit a dead end at setup with no first-class alternative.

Happy to open a PR for this. Want to align on the interface shape before building — does packages/payments/ feel like the right home, or would you prefer separate addon packages per provider?