feat: add Google Sign-In to login and register pages

- Add GoogleOAuthProvider wrapper in layout.tsx
- Add Google login button to LoginForm with "or continue with email" separator
- Add Google signup button to RegisterForm
- Add Google auth types and API client integration
- Add GOOGLE_CLIENT_ID and NEXT_PUBLIC_GOOGLE_CLIENT_ID to env config
- Add translations (EN/FR) for Google OAuth UI
- Backend already has /api/v1/auth/google endpoint, no changes needed

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/app/layout.tsx

@@ -6,6 +6,7 @@ import { ThemeProvider } from "@/providers/ThemeProvider";
 import { NotificationProvider } from "@/components/ui/notification";
 import { I18nProvider } from "@/lib/i18n";
 import { Agentation } from "agentation";
+import { GoogleOAuthProvider } from "@react-oauth/google";
 
 export const dynamic = 'force-dynamic';
 
@@ -29,9 +30,11 @@ export default function RootLayout({
         <ThemeProvider attribute="class" defaultTheme="system" enableSystem={true} disableTransitionOnChange={false}>
           <I18nProvider>
             <QueryProvider>
-              <NotificationProvider>
-                {children}
-              </NotificationProvider>
+              <GoogleOAuthProvider clientId={process.env.NEXT_PUBLIC_GOOGLE_CLIENT_ID || ""}>
+                <NotificationProvider>
+                  {children}
+                </NotificationProvider>
+              </GoogleOAuthProvider>
             </QueryProvider>
           </I18nProvider>
           {process.env.NODE_ENV === "development" && <Agentation />}