feat: Implement registry for meta plugins

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/meta_plugin/user.rs

@@ -95,3 +95,13 @@ impl MetaPlugin for UserMetaPlugin {
         self.base.options_mut()
     }
 }
+use crate::meta_plugin::register_meta_plugin;
+use crate::meta_plugin::MetaPluginType;
+
+// Register the plugin at module initialization time
+#[ctor::ctor]
+fn register_user_plugin() {
+    register_meta_plugin(MetaPluginType::User, |options, outputs| {
+        Box::new(UserMetaPlugin::new(options, outputs))
+    });
+}