refactor: port admin activation resend to the email outbox

develop replaced direct IEmailService sends with the durable EmailOutbox,
where the activation token is minted by the consumer at send time rather
than by the caller. Re-express ResendActivationEmailAsync in those terms:
seed a token hash when the activation request is missing and enqueue
EmailOutboxMessage.ForAccountActivation instead of calling _emailService
with a self-minted token.

The outbox coalesce key supersedes any pending activation for the user, so
the explicit EmailSendAttempts bookkeeping is no longer needed.

Author: hhvrc

API/Services/Account/AccountService.cs

@@ -274,29 +274,23 @@ public async Task<OneOf<Success, AccountAlreadyActivated, AccountDeactivated, No
         if (user.UserDeactivation is not null) return new AccountDeactivated();
         if (user.ActivatedAt is not null) return new AccountAlreadyActivated();
 
-        var token = CryptoUtils.RandomAlphaNumericString(AuthConstants.GeneratedTokenLength);
-        var tokenHash = HashingUtils.HashToken(token);
-
         if (user.UserActivationRequest is null)
         {
-            // Legacy / OAuth-trusted accounts may never have had an activation request created.
+            // Legacy / OAuth-trusted accounts may never have had an activation request created. The real
+            // token is minted by the outbox consumer at send time, so only seed the hash here.
             user.UserActivationRequest = new UserActivationRequest
             {
                 UserId = user.Id,
-                TokenHash = tokenHash,
-                EmailSendAttempts = 1
+                TokenHash = SeedTokenHash()
             };
         }
-        else
-        {
-            user.UserActivationRequest.TokenHash = tokenHash;
-            user.UserActivationRequest.EmailSendAttempts++;
-        }
 
-        await _db.SaveChangesAsync(cancellationToken);
+        // Durably enqueue the activation email. Its coalesce key supersedes any still-pending activation
+        // for this user, and the consumer re-mints the token on send, invalidating previously sent links.
+        _db.EmailOutbox.Add(EmailOutboxMessage.ForAccountActivation(user.Id, user.Email, user.Name));
 
-        await _emailService.ActivateAccount(new Contact(user.Email, user.Name),
-            new Uri(_frontendConfig.BaseUrl, $"/activate?token={token}"), cancellationToken);
+        await _db.SaveChangesAsync(cancellationToken);
+        await NotifyEmailOutboxAsync();
 
         return new Success();
     }