feat(i18n): add Farsi (fa) locale for app, UI, and desktop

[pourmirzai]

Issue for this PR

Builds on localization work in #37184 (docs/README/glossary fa) and #34396 (closed), fills the app/UI/desktop locale gap left by auto-closed #33338.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds full Persian (Farsi, fa) locale support for non-terminal surfaces — app web UI, shared UI components, and desktop Electron wrapper — with complete key/placeholder parity, adapted to the new centralized locale structure introduced in dev.

Files changed (9):

• packages/app/src/i18n/fa.ts (new, 996 keys, 1104 lines)
• packages/ui/src/i18n/fa.ts (new, 171 keys)
• packages/desktop/src/renderer/i18n/fa.ts (new, 21 keys)
• packages/app/src/i18n/en.ts (+language.fa: فارسی)
• packages/app/src/i18n/desktop-native.ts (+fa to DESKTOP_NATIVE_LOCALES)
• packages/app/src/context/language.tsx (RTL, INTL, LABEL_KEY, loaders, localeMatchers)
• packages/desktop/src/renderer/i18n/index.ts (imports, detectLocale, build)
• packages/app/src/i18n/parity.test.ts (+fa to ^GppLocales)
• script/translate-app.ts (+a: Farsi)

All locale registrations follow the new centralized structure from recent i18n refactors (desktop-native.ts locale source of truth, RTL_LOCALES for direction detection, etc.).

Key parity verified: standalone bun script confirms 996/996 (app), 171/171 (ui), 21/21 (desktop) with 0 placeholder mismatches.

How did you verify your code works?

• Typecheck passes for packages/app and packages/desktop (tsgo -b)
• Parity verified via standalone bun module import: 0 missing, 0 extra keys, 0 placeholder mismatches
• Locale registration follows existing patterns (all loaders, localeMatchers, RTL_LOCALES updated)

Note: The official parity.test.ts is skipIf(CI) and may report drift due to pre-existing gaps in other locales (not introduced by fa).

Screenshots / recordings

N/A (i18n strings only — no UI layout changes; RTL already partially implemented in dev)

Checklist

• I have tested my changes locally (typecheck verified; desktop/web runtime testing deferred)
• I have not included unrelated changes in this PR (9 files, all i18n-related)

If you do not follow this template your PR will be automatically rejected.

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