fix: ignore unmatched YAML properties in PluginSettings

Prevents deserialization crash when config file contains keys from newer plugin versions.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

MosswartMassacre/PluginSettings.cs

@@ -65,7 +65,8 @@ namespace MosswartMassacre
 
             // build serializer/deserializer once
             var builder = new DeserializerBuilder()
-                .WithNamingConvention(UnderscoredNamingConvention.Instance);
+                .WithNamingConvention(UnderscoredNamingConvention.Instance)
+                .IgnoreUnmatchedProperties();
             var deserializer = builder.Build();
 
             PluginSettings loaded = null;