feat: add per-account connection/subscription limits with AccountConfig

src/NATS.Server/NatsOptions.cs

@@ -29,6 +29,9 @@ public sealed class NatsOptions
     // Server tags (exposed via /varz)
     public Dictionary<string, string>? Tags { get; set; }
 
+    // Account configuration
+    public Dictionary<string, AccountConfig>? Accounts { get; set; }
+
     // Simple auth (single user)
     public string? Username { get; set; }
     public string? Password { get; set; }