feat: add max_len support to ColumnConfig and default list format

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

src/modes/list.rs

@@ -84,7 +84,7 @@ pub fn mode_list(
                 .unwrap_or_else(|_| panic!("Unknown column {:?}", column.name));
 
             let mut meta_name: Option<&str> = None;
-            let column_width = 0; // We're not supporting width in the new format
+            let column_width = column.max_len.unwrap_or(0);
 
             if let ColumnType::Meta = column_type {
                 let parts: Vec<&str> = column.name.split(':').collect();