feat: update digest and system plugins to return PluginResponse

Co-authored-by: aider (openai/andrew/openrouter/mistralai/mistral-medium-3.1) <aider@aider.chat>

src/meta_plugin/system.rs

@@ -174,11 +174,18 @@ impl MetaPlugin for UidMetaPlugin {
         self.meta_name.clone()
     }
     
-    fn initialize(&mut self, conn: &Connection, item_id: i64) -> Result<()> {
+    fn initialize(&mut self, item_id: i64) -> Result<PluginResponse> {
+        let mut metadata = Vec::new();
         let uid = get_current_uid().to_string();
-        self.save_meta(conn, item_id, "uid", uid)?;
-        self.is_saved = true;
-        Ok(())
+
+        if let Some(meta) = self.create_meta(item_id, "uid", uid) {
+            metadata.push(meta);
+        }
+
+        Ok(PluginResponse {
+            metadata: Some(metadata),
+            is_finalized: true,
+        })
     }
     
     fn outputs(&self) -> &std::collections::HashMap<String, serde_yaml::Value> {