feat: implement OAuth 2.0 / OpenID Connect support

- Added OAuth configuration management in the admin panel.
- Implemented OAuth authorization flow with PKCE for enhanced security.
- Created routes for handling OAuth provider discovery, authorization, and callback.
- Integrated OAuth login and registration options in the frontend.
- Updated UI components to support OAuth login and registration.
- Added internationalization strings for OAuth-related messages.
- Implemented encryption for client secrets and secure state management.
- Added error handling and user feedback for OAuth processes.

src/pages/OAuthCallback.jsx

@@ -0,0 +1,75 @@
+import { useEffect, useState } from 'react';
+import { useNavigate, useSearchParams } from 'react-router-dom';
+import { useAuth } from '../contexts/AuthContext';
+import { useLanguage } from '../contexts/LanguageContext';
+import { Loader2, AlertTriangle } from 'lucide-react';
+import toast from 'react-hot-toast';
+
+export default function OAuthCallback() {
+  const [searchParams] = useSearchParams();
+  const [error, setError] = useState(null);
+  const { loginWithOAuth } = useAuth();
+  const { t } = useLanguage();
+  const navigate = useNavigate();
+
+  useEffect(() => {
+    const token = searchParams.get('token');
+    const errorMsg = searchParams.get('error');
+    const returnTo = searchParams.get('return_to') || '/dashboard';
+
+    if (errorMsg) {
+      setError(errorMsg);
+      return;
+    }
+
+    if (!token) {
+      setError(t('auth.oauthNoToken'));
+      return;
+    }
+
+    // Store token and redirect
+    loginWithOAuth(token)
+      .then(() => {
+        toast.success(t('auth.loginSuccess'));
+        navigate(returnTo, { replace: true });
+      })
+      .catch(() => {
+        setError(t('auth.oauthLoginFailed'));
+      });
+  }, []); // eslint-disable-line react-hooks/exhaustive-deps
+
+  if (error) {
+    return (
+      <div className="min-h-screen flex items-center justify-center p-6">
+        <div className="absolute inset-0 bg-th-bg" />
+        <div className="relative w-full max-w-md">
+          <div className="card p-8 backdrop-blur-xl bg-th-card/80 border border-th-border shadow-2xl rounded-2xl text-center">
+            <div className="flex justify-center mb-4">
+              <div className="w-12 h-12 bg-red-500/20 rounded-full flex items-center justify-center">
+                <AlertTriangle size={24} className="text-red-400" />
+              </div>
+            </div>
+            <h2 className="text-xl font-bold text-th-text mb-2">{t('auth.oauthError')}</h2>
+            <p className="text-th-text-s mb-6">{error}</p>
+            <button
+              onClick={() => navigate('/login', { replace: true })}
+              className="btn-primary w-full py-3"
+            >
+              {t('auth.backToLogin')}
+            </button>
+          </div>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="min-h-screen flex items-center justify-center p-6">
+      <div className="absolute inset-0 bg-th-bg" />
+      <div className="relative flex flex-col items-center gap-4">
+        <Loader2 size={32} className="animate-spin text-th-accent" />
+        <p className="text-th-text-s">{t('auth.oauthRedirecting')}</p>
+      </div>
+    </div>
+  );
+}