feat(desktop): add i18n infrastructure with French (fr) support

[Foolafroos]

Summary

Adds a scalable internationalization (i18n) layer to the Hermes Agent desktop app, with complete French (fr) support. The architecture is designed so additional languages can be added by simply dropping in a new .json file — zero refactoring required.

What changed

New files

File	Purpose
apps/desktop/src/i18n/context.tsx	I18nProvider React Context + useTranslation() hook. Lazy-loads locale bundles, falls back to EN, persists choice in localStorage with browser language detection.
apps/desktop/src/i18n/index.ts	Barrel exports
apps/desktop/src/i18n/messages/en.json	270 keys — source of truth, extracted from all hardcoded UI strings
apps/desktop/src/i18n/messages/fr.json	270 keys — complete French translation (100% parity with EN)
apps/desktop/src/i18n/language-selector.tsx	Standalone LanguageSelector component (unused — language dropdown is built directly into titlebar for subtlety)

Modified files

File	Change
apps/desktop/src/main.tsx	Wired <I18nProvider> above <ThemeProvider> in the root tree
apps/desktop/src/app/shell/titlebar-controls.tsx	Added LanguageDropdown — subtle locale code button (e.g. EN / FR) in the titlebar system tools, between haptics and settings
apps/desktop/src/components/chat/intro.tsx	Added bilingual fallback copy (EN + FR entries in the intro message pool)

Architecture

I18nProvider (context)
  ├── locale detection: localStorage → browser navigator → "en" fallback
  ├── lazy bundle loading: dynamic import().then(m => m.default)
  ├── useTranslation() hook: t(key, params) with interpolation
  └── LanguageDropdown: titlebar integration, no modals, no onboarding

• No heavy i18n library — custom React Context keeps bundle size minimal
• Adding a new language = add XX.json to messages/ + one line in LOCALES array
• Desktop locale preference persists across sessions via localStorage

Validation

• ✅ tsc -b — zero TypeScript errors
• ✅ 270/270 keys parity between en.json and fr.json
• ✅ Backend locales/en.yaml ↔ locales/fr.yaml already aligned

Screenshots

The language selector appears as a subtle locale code in the titlebar:

[ ... ]  [🔔]  [EN ▼]  [⚙️]

Clicking it opens a dropdown to switch between English and Français.

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Note: This PR only wires the infrastructure and translates the UI layer. Replacing every individual hardcoded string with t("key") calls across all 1200+ JSX text nodes is a follow-up — but the system is ready to consume them.

[teknium1]

Thanks for the French translation work. Current main already has a typed, config-backed desktop i18n system, while French itself is still not registered.

Problems

• This patch adds a second i18n implementation instead of extending the current contract: apps/desktop/src/i18n/context.tsx:107-146 persists display.language, types.ts:8 defines supported locales, and catalog.ts:7-12 registers locale tables. The PR's JSON/localStorage provider conflicts with that architecture.
• The diff only invokes the new string-key t(...) API in the titlebar dropdown; its LanguageSelector is unused. Therefore the bundled French JSON does not translate the broader current UI, consistent with the PR body noting that JSX migration is deferred.
• No tests cover French locale normalization, config persistence, or runtime fallback; existing conventions are in apps/desktop/src/i18n/context.test.tsx:60-76,155-230 and runtime.test.ts:18-74.

Suggested changes

• Salvage the French copy as a typed fr locale registered through types.ts, languages.ts, and catalog.ts, using the existing provider and display.language persistence.
• Add French coverage alongside the existing context and runtime tests.

This is an automated hermes-sweeper review.

[teknium1]

Current main already has a config-backed I18nProvider and typed locale catalog. Please extend that contract with fr rather than adding a second JSON/dynamic-import provider; otherwise this conflicts with the established display.language persistence path.