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

prisma/schema.prisma

@@ -86,6 +86,7 @@ model User {
   id           String   @id @default(cuid())
   email        String   @unique
   passwordHash String?
+  googleId     String?  @unique
   name         String?
   avatarUrl    String?
   role         UserRole @default(USER)