feat: add Google OAuth sign-in button to login page

Users can now sign in with their Google account via Supabase OAuth.
Google button appears above wallet connect in the "Or continue with" section.

web/src/pages/Login.tsx

@@ -2,6 +2,7 @@ import { useState } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useAuth } from '@/contexts/AuthContext';
 import { usePezkuwi } from '@/contexts/PezkuwiContext';
+import { supabase } from '@/lib/supabase';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
@@ -121,6 +122,26 @@ const Login: React.FC = () => {
     }
   };
 
+  const handleGoogleSignIn = async () => {
+    setError('');
+    setLoading(true);
+    try {
+      const { error } = await supabase.auth.signInWithOAuth({
+        provider: 'google',
+        options: {
+          redirectTo: window.location.origin + '/',
+        },
+      });
+      if (error) {
+        setError(error.message);
+      }
+    } catch {
+      setError('Google sign-in failed. Please try again.');
+    } finally {
+      setLoading(false);
+    }
+  };
+
   return (
     <div className="min-h-screen bg-gradient-to-br from-gray-900 via-black to-gray-900 flex items-center justify-center p-4">
       <div className="absolute inset-0 bg-[url('/grid.svg')] bg-center [mask-image:linear-gradient(180deg,white,rgba(255,255,255,0))]"></div>
@@ -360,19 +381,32 @@ const Login: React.FC = () => {
             </div>
           </div>
           
-          <Button
-            variant="outline"
-            className="w-full border-gray-700 bg-gray-800 hover:bg-gray-700 text-white"
-            onClick={handleWalletConnect}
-            disabled={loading}
-          >
-            <Wallet className="mr-2 h-4 w-4" />
-            {t('login.connectWallet', 'Connect with Pezkuwi.js')}
-          </Button>
+          <div className="space-y-3">
+            <Button
+              variant="outline"
+              className="w-full border-gray-700 bg-gray-800 hover:bg-gray-700 text-white"
+              onClick={handleGoogleSignIn}
+              disabled={loading}
+            >
+              <svg className="mr-2 h-4 w-4" viewBox="0 0 24 24">
+                <path fill="#4285F4" d="M22.56 12.25c0-.78-.07-1.53-.2-2.25H12v4.26h5.92a5.06 5.06 0 0 1-2.2 3.32v2.77h3.57c2.08-1.92 3.28-4.74 3.28-8.1z" />
+                <path fill="#34A853" d="M12 23c2.97 0 5.46-.98 7.28-2.66l-3.57-2.77c-.98.66-2.23 1.06-3.71 1.06-2.86 0-5.29-1.93-6.16-4.53H2.18v2.84C3.99 20.53 7.7 23 12 23z" />
+                <path fill="#FBBC05" d="M5.84 14.09c-.22-.66-.35-1.36-.35-2.09s.13-1.43.35-2.09V7.07H2.18C1.43 8.55 1 10.22 1 12s.43 3.45 1.18 4.93l2.85-2.22.81-.62z" />
+                <path fill="#EA4335" d="M12 5.38c1.62 0 3.06.56 4.21 1.64l3.15-3.15C17.45 2.09 14.97 1 12 1 7.7 1 3.99 3.47 2.18 7.07l3.66 2.84c.87-2.6 3.3-4.53 6.16-4.53z" />
+              </svg>
+              {t('login.googleSignIn', 'Continue with Google')}
+            </Button>
 
-          <p className="mt-2 text-xs text-center text-gray-500">
-            {t('login.walletHint', 'Connect your Pezkuwi.js for instant access')}
-          </p>
+            <Button
+              variant="outline"
+              className="w-full border-gray-700 bg-gray-800 hover:bg-gray-700 text-white"
+              onClick={handleWalletConnect}
+              disabled={loading}
+            >
+              <Wallet className="mr-2 h-4 w-4" />
+              {t('login.connectWallet', 'Connect with Pezkuwi.js')}
+            </Button>
+          </div>
         </CardContent>
         
         <CardFooter className="text-center text-sm text-gray-500">