receiptI18n: Add RTL language support flag and direction helpers

[Kingsman-99]

Description

receiptI18n provides localised strings for payment receipts but does not indicate whether the active locale uses right-to-left text direction. Contributors should add an isRtl(locale: string): boolean helper and a per-locale rtl: boolean metadata field so receipt rendering code can apply dir="rtl" and mirror layout accordingly.

Acceptance Criteria

• An isRtl(locale: string): boolean function is exported that returns true for RTL locales (ar, he, fa, ur at minimum)
• Each locale entry in the translation map includes an rtl: boolean metadata field
• A getReceiptDirection(locale: string): "ltr" | "rtl" convenience function is also exported
• Existing tests continue to pass

Context

• Target file: src/lib/receiptI18n.ts
• i18n types: src/lib/i18nTypes.ts

[guptakumarranjeet150]

Hi everyone,

I would like to resolve this issue. Here is my proposed execution plan:

• Implementation: Deliver a clean, modular solution for receiptI18n: Add RTL language support flag and direction helpers strictly following Stellar-split/split-app conventions.
• Testing & Verification: Cover changes with automated tests ensuring CI passes smoothly.
• Delivery: Ready to ship a thoroughly tested PR within 12–24 hours with passing CI.

Looking forward to contributing—please feel free to assign!