Add impersonatedBy field to Session model for admin plugin

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/schema.prisma

@@ -36,14 +36,15 @@ model User {
 }
 
 model Session {
-  id        String   @id @default(cuid())
-  userId    String
-  token     String   @unique
-  expiresAt DateTime
-  ipAddress String?
-  userAgent String?
-  createdAt DateTime @default(now())
-  updatedAt DateTime @updatedAt
+  id             String   @id @default(cuid())
+  userId         String
+  token          String   @unique
+  expiresAt      DateTime
+  ipAddress      String?
+  userAgent      String?
+  impersonatedBy String?
+  createdAt      DateTime @default(now())
+  updatedAt      DateTime @updatedAt
 
   user User @relation(fields: [userId], references: [id], onDelete: Cascade)
 }