feat(i18n): add Persian/Farsi and Iran support

[khaira777]

Context

Discussion: https://github.com/orgs/FreeOpenSourcePOS/discussions/239

A community member requested Persian/Farsi support and suggested adding Iran to the country profile. This issue tracks the work without treating a country entry as complete language support.

Goal

Provide a reliable first-class experience for Iranian businesses using Persian (fa-IR) and the Iran (IR) country profile.

Scope

• Add the Iran country profile with verified locale, currency, timezone, and dialing information.
• Add Persian/Farsi as a supported UI language.
• Add a complete Persian translation with the same key coverage as the existing languages.
• Add RTL document and layout support, including setup, dashboard, POS, KDS, and settings.
• Verify Persian date, number, currency, and text rendering.
• Test browser receipts and thermal receipts with Persian text where the printer supports it.
• Confirm the correct Iranian business identifier terminology before choosing the tax registration label. Rial is a currency, not a tax identifier.

Delivery checklist

• Confirm terminology with an Iranian business user or accountant (شناسه ملی, کد اقتصادی, or another appropriate identifier).
• Add IR to the shared country profile (fa-IR, IRR, Asia/Tehran, +98).
• Add fa to the language types, setup flow, settings, server/KDS metadata, and HTML language handling.
• Add fa.json and pass translation key-integrity checks.
• Implement and visually verify RTL behavior across the main application surfaces.
• Verify currency and number formatting, including the Rial/Toman distinction. Do not silently convert between units.
• Verify browser printing and document direction.
• Verify thermal printer encoding, Persian shaping, RTL order, and fallback behavior.
• Add focused tests and update documentation.

Out of scope for the initial language/country contribution

• This issue does not by itself promise official Iranian tax compliance or a complete Iranian tax pack. Tax rules should be added separately after they are verified.
• Payment-provider, fiscal e-invoicing, and other Iran-specific integrations are separate work.

Contribution notes

This is broad enough to be split into smaller pull requests after someone takes ownership. A contributor who can provide or review native Persian translations and local tax terminology would be especially valuable. The initial implementation should avoid shipping a partial translation or an untested RTL layout as if support were complete.

Acceptance criteria

• Persian can be selected during setup and in settings, persists server-side, and is inherited by the standalone KDS.
• The main POS flows do not expose raw translation keys and render correctly in RTL.
• Country selection for Iran supplies the expected locale, currency, timezone, and phone dial code.
• Dates, amounts, and receipts are tested for the chosen Rial/Toman behavior.
• Unsupported printer capabilities fail safely or use a documented fallback.
• Existing English, Spanish, and Portuguese behavior remains unchanged.