feat: make save_item return only item ID for CLI usage

Co-authored-by: aider (openai/andrew/openrouter/anthropic/claude-sonnet-4) <aider@aider.chat>

src/modes/save.rs

@@ -51,7 +51,7 @@ pub fn mode_save(
         writer: stdout.lock(),
     };
 
-    item_service.save_item(tee_reader, cmd, settings, tags, conn)?;
+    let _item_id = item_service.save_item(tee_reader, cmd, settings, tags, conn)?;
 
     Ok(())
 }