refactor: rename core module to services

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

src/modes/delete.rs

@@ -2,8 +2,8 @@ use anyhow::{anyhow, Result};
 use std::path::PathBuf;
 
 use crate::config;
-use crate::core::error::CoreError;
-use crate::core::item_service::ItemService;
+use crate::services::error::CoreError;
+use crate::services::item_service::ItemService;
 use clap::error::ErrorKind;
 use clap::Command;
 use log::warn;