feat: update instructor search to exclude self and existing course instructors, add email_verified_at to user responses

Update searchInstructors endpoint to accept courseId parameter and filter out the requesting instructor and instructors already assigned to the course. Add email_verified_at field to UserResponse type and include it in auth and user service responses.

Backend/src/services/auth.service.ts

@@ -398,6 +398,7 @@ export class AuthService {
             id: user.id,
             username: user.username,
             email: user.email,
+            email_verified_at: user.email_verified_at,
             updated_at: user.updated_at,
             created_at: user.created_at,
             role: {
@@ -423,6 +424,7 @@ export class AuthService {
             id: user.id,
             username: user.username,
             email: user.email,
+            email_verified_at: user.email_verified_at,
             updated_at: user.updated_at,
             created_at: user.created_at,
             role: {