fix: add missing serde default to list_format field

Fixes deserialization failure in generate-config mode by adding
#[serde(default)] attribute to list_format field in Settings struct.
This allows the config library to provide sensible defaults when
no config file exists, resolving the error "missing field list_format".

Also unstages AGENT.md naming change since that's a different fix.

src/config.rs

@@ -170,6 +170,7 @@ pub struct MetaPluginConfig {
 pub struct Settings {
     #[serde(default)]
     pub dir: PathBuf,
+    #[serde(default)]
     pub list_format: Vec<ColumnConfig>,
     #[serde(default)]
     pub table_config: TableConfig,