👔 Prevent duplicate contact method

DysonNetwork.Pass/Account/AccountService.cs

@@ -88,6 +88,12 @@ public class AccountService(
         if (dupeNameCount > 0)
             throw new InvalidOperationException("Account name has already been taken.");
 
+        var dupeEmailCount = await db.AccountContacts
+            .Where(c => c.Content == email && c.Type == AccountContactType.Email
+            ).CountAsync();
+        if (dupeEmailCount > 0)
+            throw new InvalidOperationException("Account email has already been used.");
+
         var account = new Account
         {
             Name = name,
@@ -504,6 +510,12 @@ public class AccountService(
 
     public async Task<AccountContact> CreateContactMethod(Account account, AccountContactType type, string content)
     {
+        var isExists = await db.AccountContacts
+            .Where(x => x.AccountId == account.Id && x.Type == type && x.Content == content)
+            .AnyAsync();
+        if (isExists)
+            throw new InvalidOperationException("Contact method already exists.");
+        
         var contact = new AccountContact
         {
             Type = type,