Refactor IPC and DTO structures; remove unused code and streamline message handling

- Removed unused structs and methods from `response.rs`, `usage.rs`, and `client.rs`.
- Simplified `Connection` handling in `conn.rs` to only support Unix sockets.
- Updated `IpcServer` to exclusively use Unix sockets and removed TCP handling.
- Cleaned up `editlog.rs` by removing loading and recent entry methods.
- Refactored `memory.rs` to eliminate unused functions related to lesson promotion and retrospective creation.
- Enhanced `search.rs` to support multiple search providers and improved error handling.
- Updated chat view logic to simplify message display and improve user experience.
- Removed deprecated modules and constants from various files to streamline the codebase.

src/model/session.rs

@@ -41,14 +41,6 @@ impl Session {
         self.session_dir(base_dir).join("conversation.json")
     }
 
-    pub fn edit_log_path(&self, base_dir: &Path) -> PathBuf {
-        self.session_dir(base_dir).join("edits.jsonl")
-    }
-
-    pub fn msglog_path(&self, base_dir: &Path) -> PathBuf {
-        self.session_dir(base_dir).join("msglog.db")
-    }
-
     pub fn save(&self, base_dir: &Path) -> std::io::Result<()> {
         let dir = self.session_dir(base_dir);
         std::fs::create_dir_all(&dir)?;