fix: remove php-fpm pool on account creation rollback to prevent fpm crash

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LP9Q4kfCAYAjJnsbHBrViZ

panel/lib/AccountManager.php

@@ -65,8 +65,9 @@ class AccountManager {
             $db->commit();
         } catch (Throwable $e) {
             $db->rollBack();
-            // Clean up Linux user if DB failed
+            // Clean up Linux user and PHP-FPM pool so orphaned configs can't crash php-fpm
             self::shell("userdel -r " . escapeshellarg($username) . " 2>/dev/null || true");
+            PHPManager::removePool($username);
             throw $e;
         }