feat: add read time tracking functionality

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

src/meta_plugin/digest.rs

@@ -170,13 +170,30 @@ impl MetaPlugin for ReadTimeMetaPlugin {
     }
     
     fn finalize(&mut self) -> Result<PluginResponse> {
-        Ok(PluginResponse::default())
+        let mut metadata = Vec::new();
+
+        if let Some(start_time) = self.start_time {
+            if let Some(item_id) = self.item_id {
+                let duration = start_time.elapsed();
+                let duration_str = format!("{:.3} seconds", duration.as_secs_f64());
+
+                if let Some(meta) = self.create_meta(item_id, "read_time", duration_str) {
+                    metadata.push(meta);
+                }
+            }
+        }
+
+        Ok(PluginResponse {
+            metadata: Some(metadata),
+            is_finalized: true,
+        })
     }
 
     fn update(&mut self, _data: &[u8]) -> Result<PluginResponse> {
         if self.start_time.is_none() {
             self.start_time = Some(Instant::now());
         }
+        Ok(PluginResponse::default())
     }
 
     fn meta_name(&self) -> String {