feat: Google OAuth ile giris

- User modeline googleId (unique) eklendi
- google start/callback API route'lari (state korumali, find-or-create)
- Login/register sayfalarina Google butonu
- docker-compose'a GOOGLE_CLIENT_ID/SECRET env gecisi
- tsconfig.tsbuildinfo gitignore'a eklendi

src/app/register/page.tsx

@@ -2,6 +2,17 @@
 
 import { useState } from "react";
 
+function GoogleIcon() {
+  return (
+    <svg width="18" height="18" viewBox="0 0 48 48" aria-hidden="true">
+      <path fill="#EA4335" d="M24 9.5c3.54 0 6.71 1.22 9.21 3.6l6.85-6.85C35.9 2.38 30.47 0 24 0 14.62 0 6.51 5.38 2.56 13.22l7.98 6.19C12.43 13.72 17.74 9.5 24 9.5z" />
+      <path fill="#4285F4" d="M46.98 24.55c0-1.57-.15-3.09-.38-4.55H24v9.02h12.94c-.58 2.96-2.26 5.48-4.78 7.18l7.73 6c4.51-4.18 7.09-10.36 7.09-17.65z" />
+      <path fill="#FBBC05" d="M10.53 28.59c-.48-1.45-.76-2.99-.76-4.59s.27-3.14.76-4.59l-7.98-6.19C.92 16.46 0 20.12 0 24c0 3.88.92 7.54 2.56 10.78l7.97-6.19z" />
+      <path fill="#34A853" d="M24 48c6.48 0 11.93-2.13 15.89-5.81l-7.73-6c-2.15 1.45-4.92 2.3-8.16 2.3-6.26 0-11.57-4.22-13.47-9.91l-7.98 6.19C6.51 42.62 14.62 48 24 48z" />
+    </svg>
+  );
+}
+
 export default function RegisterPage() {
   const [email, setEmail] = useState("");
   const [password, setPassword] = useState("");
@@ -54,8 +65,19 @@ export default function RegisterPage() {
         />
         
         {error && <div className="mt-4 rounded-xl bg-red-50 p-3 text-sm text-red-700">{error}</div>}
+
+        <a href="/api/auth/google/start" className="mt-6 flex w-full items-center justify-center gap-3 rounded-xl border border-slate-200 bg-white px-4 py-3 font-semibold text-slate-700 transition hover:bg-slate-50">
+          <GoogleIcon />
+          Google ile devam et
+        </a>
         
-        <button className="mt-6 w-full rounded-xl bg-violet-700 px-4 py-3 font-bold text-white hover:bg-violet-800 transition">
+        <div className="mt-4 flex items-center gap-3">
+          <div className="h-px flex-1 bg-slate-200" />
+          <span className="text-xs font-medium text-slate-400">veya</span>
+          <div className="h-px flex-1 bg-slate-200" />
+        </div>
+        
+        <button className="mt-4 w-full rounded-xl bg-violet-700 px-4 py-3 font-bold text-white hover:bg-violet-800 transition">
           Hesap oluştur
         </button>