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

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

What does this PR does

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.

Files changed:

• packages/app/src/i18n/fa.ts (996 keys, 1104 lines)
• packages/ui/src/i18n/fa.ts (171 keys)
• packages/desktop/src/renderer/i18n/fa.ts (21 keys)
• packages/app/src/context/language.tsx (Locale union, LOCALES, INTL, LABEL_KEY, loaders, localeMatchers)
• packages/desktop/src/renderer/i18n/index.ts (imports, detectLocale, build)
• packages/app/src/i18n/en.ts + 17 other locales (language.fa: فارسی)
• packages/app/src/i18n/parity.test.ts (fa in appLocales)
• script/translate-app.ts (fa in locale registry)

otes/fa-audit.md (existing RTL PRs audit, gap analysis)

Key parity verified: 996/996 (app), 171/171 (ui), 21/21 (desktop), 0 placeholder mismatches.

Deliberate scope decisions:

• RTL layout infrastructure deferred to open PR feat(i18n): Add Hebrew language support with RTL handling #39423 (Hebrew + shared RTL)
• Chat/content bidi deferred to feat(app): support bidirectional chat text #38079/fix(app): correct RTL rendering for mixed Arabic/English content #37249
• Docs/README/glossary fa left to docs: add Farsi (fa) translations #37184 (no duplication)
• Desktop native menu localization untouched (pre-existing gap, not fa-specific)
• Console/stats app fa deferred (separate work)

How did you verify your code works

Ran official parity.test.ts with bun — all fa parity checks pass:

• ✅ placeholder preservation
• ✅ unseen session keys
• ✅ changed-file summary keys
• ✅ key parity (authoritative check via bun module import: 0 missing, 0 extra, 0 placeholder mismatches across app/ui/desktop)

Note: parity.test.ts fails on �r locale (5 missing keys: dialog.provider.custom.label, dialog.model.unpaid.viewMoreProviders, session.header.reveal.finder/fileExplorer/containingFolder). This is a pre-existing gap in dev, unrelated to fa.

Screenshots / recordings

N/A (i18n strings only — no UI layout changes; RTL will follow via #39423).

Checklist

• I have tested my changes locally (parity verified via bun; desktop/web runtime testing deferred)
• I have not included unrelated changes in this PR (26 files, all i18n-related)

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.
• Not all checklist items are checked. Please confirm you have tested locally and have not included unrelated changes.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

The search results show PR #40386 (the current PR) and related but distinct PRs that are intentionally scoped separately:

• docs: add Farsi (fa) translations #37184 (docs: add Farsi translations) - covers docs/README/glossary only
• feat(i18n): Add Hebrew language support with RTL handling #39423 (Hebrew language support with RTL) - handles RTL infrastructure deferred from this PR

[pourmirzai]

Will resubmit on updated dev base