fix: implement default config path logic and remove unused variable warning

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/modes/list.rs

@@ -87,7 +87,7 @@ pub fn mode_list(
     let mut title_row = row!();
 
     for column in &settings.list_format {
-        let column_type = ColumnType::from_str(&column.name)
+        let _column_type = ColumnType::from_str(&column.name)
             .map_err(|_| anyhow!("Unknown column {:?}", column.name))?;
 
         title_row.add_cell(Cell::new(&column.label).with_style(Attr::Bold));