feat: enhance user validation and center owner checks in CenterMentorSchema

- Updated the CenterMentorSchema to include user validation by fetching user information based on email.
- Implemented error handling to throw an error if the user is not found.
- Modified the logic to block center owners from being invited as mentors by checking against the user's ID instead of the email.
- Improved overall error messaging for better clarity when invitation conditions are not met.

src/CenterMentor/centermentor.schema.ts

@@ -147,9 +147,16 @@ export class CenterMentorSchema extends PothosSchema {
             if (!userId) {
               throw new Error('User ID is required')
             }
-            // block invite center owner
-            const centerOwner = await prisma.center.findUnique({
-              where: { centerOwnerId: userId },
+            // get user info
+            const user = await prisma.user.findUnique({
+              where: { email: args.email },
+            })
+            if (!user) {
+              throw new Error('User not found')
+            }
+            // block invite center owner from another center
+            const centerOwner = await prisma.center.findFirst({
+              where: { centerOwnerId: user.id },
             })
             if (centerOwner) {
               throw new Error('Center owner cannot be invited as a mentor')