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