docs: FAQ - 3-decimal and 0-decimal currencies not supported for invoices

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Summary

Adds a public documentation FAQ clarifying that Razorpay Invoices do not support 3-decimal and 0-decimal currencies (e.g. KWD, OMR, BHD, JOD, LYD, TND for 3-decimal; JPY, IDR for 0-decimal), as requested by the support/cross-border team (ref ISS-1536032 / ISS-3645601).

Changes

• payments/international-payments/faqs.md — new FAQ #11 ''Can I create invoices in 3-decimal or 0-decimal currencies?'' (placed in the international/cross-border section as requested).
• payments/invoices/faqs.md — updated FAQ Made changes in scripts #2 ''Can I raise invoices in international currency?'' to cross-reference the new limitation, since the previous wording (''any of the supported international currencies'') contradicted it.

Context

Unlike 2-decimal currencies (e.g. INR, USD), 3-decimal and 0-decimal currencies cannot be used to create invoices. Invoice creation in these currencies is disabled in the Razorpay Dashboard; merchants must convert to a supported 2-decimal currency instead.