fix: clarify school_roll_number validation message for backend logging

Author: Mohamed-RPF

config/locales/en.yml

@@ -14,7 +14,7 @@ en:
   validations:
     school:
       website: "must be a valid URL"
-      school_roll_number: "must be alphanumeric (e.g., 01572D)"
+      school_roll_number: "must be numbers followed by letters (e.g., 01572D)"
     invitation:
       email_address: "'%<value>s' is invalid"
   activerecord:

spec/models/school_spec.rb

@@ -167,27 +167,27 @@
       expect(school).to be_valid
     end
 
-    it 'accepts a school_roll_number with multiple letters' do
+    it 'accepts a school_roll_number with one or more letters' do
       school.school_roll_number = '12345ABC'
       expect(school).to be_valid
     end
 
     it 'rejects a school_roll_number with only numbers' do
       school.school_roll_number = '01572'
       expect(school).not_to be_valid
-      expect(school.errors[:school_roll_number]).to include('must be alphanumeric (e.g., 01572D)')
+      expect(school.errors[:school_roll_number]).to include('must be numbers followed by letters (e.g., 01572D)')
     end
 
     it 'rejects a school_roll_number with only letters' do
       school.school_roll_number = 'ABCDE'
       expect(school).not_to be_valid
-      expect(school.errors[:school_roll_number]).to include('must be alphanumeric (e.g., 01572D)')
+      expect(school.errors[:school_roll_number]).to include('must be numbers followed by letters (e.g., 01572D)')
     end
 
     it 'rejects a school_roll_number with special characters' do
       school.school_roll_number = '01572-D'
       expect(school).not_to be_valid
-      expect(school.errors[:school_roll_number]).to include('must be alphanumeric (e.g., 01572D)')
+      expect(school.errors[:school_roll_number]).to include('must be numbers followed by letters (e.g., 01572D)')
     end
 
     it 'normalizes blank school_roll_number to nil' do