refactor: rename core module to services

Co-authored-by: aider (openai/andrew/openrouter/google/gemini-2.5-pro) <aider@aider.chat>

src/modes/list.rs

@@ -1,6 +1,6 @@
 use crate::config;
-use crate::core::item_service::ItemService;
-use crate::core::types::ItemWithMeta;
+use crate::services::item_service::ItemService;
+use crate::services::types::ItemWithMeta;
 use crate::modes::common::ColumnType;
 use crate::modes::common::{size_column, string_column, OutputFormat};
 use anyhow::{Result};