feat: add i18n support (FR/EN) to backoffice with English as default

Implement full internationalization for the Next.js backoffice:
- i18n infrastructure: type-safe dictionaries (fr.ts/en.ts), cookie-based locale detection, React Context for client components, server-side translation helper
- Language selector in Settings page (General tab) with cookie + DB persistence
- All ~35 pages and components translated via t() / useTranslation()
- Default locale set to English, French available via settings

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/lib/i18n/context.tsx

@@ -0,0 +1,60 @@
+"use client";
+
+import { createContext, useContext, useCallback, useState, type ReactNode } from "react";
+import type { Locale } from "./types";
+import { LOCALE_COOKIE } from "./types";
+import { getDictionarySync, createTranslateFunction } from "./dictionaries";
+import type { TranslateFunction } from "./dictionaries";
+
+interface LocaleContextValue {
+  locale: Locale;
+  t: TranslateFunction;
+  setLocale: (locale: Locale) => void;
+}
+
+const LocaleContext = createContext<LocaleContextValue | null>(null);
+
+interface LocaleProviderProps {
+  initialLocale: Locale;
+  children: ReactNode;
+}
+
+export function LocaleProvider({ initialLocale, children }: LocaleProviderProps) {
+  const [locale] = useState<Locale>(initialLocale);
+  const dict = getDictionarySync(locale);
+  const t = createTranslateFunction(dict);
+
+  const setLocale = useCallback(async (newLocale: Locale) => {
+    // Set cookie
+    document.cookie = `${LOCALE_COOKIE}=${newLocale};path=/;max-age=${365 * 24 * 60 * 60}`;
+
+    // Save to DB
+    try {
+      const apiBase = process.env.NEXT_PUBLIC_API_URL || "http://localhost:7080";
+      await fetch(`${apiBase}/settings`, {
+        method: "PATCH",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ language: newLocale }),
+      });
+    } catch {
+      // Best effort — cookie is the primary source for rendering
+    }
+
+    // Reload to apply new locale everywhere (server + client)
+    window.location.reload();
+  }, []);
+
+  return (
+    <LocaleContext.Provider value={{ locale, t, setLocale }}>
+      {children}
+    </LocaleContext.Provider>
+  );
+}
+
+export function useTranslation(): LocaleContextValue {
+  const ctx = useContext(LocaleContext);
+  if (!ctx) {
+    throw new Error("useTranslation must be used within a LocaleProvider");
+  }
+  return ctx;
+}