fix: add @@unique on Account + VerificationToken model for NextAuth OAuth

Author: Aymanseif

prisma/schema.prisma

@@ -46,6 +46,8 @@ model Account {
   session_state      String?
 
   user               User    @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([provider, providerAccountId])
 }
 
 model Session {
@@ -90,6 +92,14 @@ model RefreshToken {
   user      User     @relation(fields: [userId], references: [id], onDelete: Cascade)
 }
 
+model VerificationToken {
+  identifier String
+  token      String   @unique
+  expires    DateTime
+
+  @@unique([identifier, token])
+}
+
 model AuditLog {
   id        String   @id @default(cuid())
   userId    String