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/dto/chat/message.rs

@@ -13,17 +13,6 @@ pub enum Role {
 }
 
 impl Role {
-    pub fn is_user(&self) -> bool {
-        matches!(self, Role::User)
-    }
-
-    pub fn is_assistant(&self) -> bool {
-        matches!(self, Role::Assistant)
-    }
-
-    pub fn is_system(&self) -> bool {
-        matches!(self, Role::System)
-    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -79,10 +68,3 @@ impl ChatMessage {
         }
     }
 }
-
-#[derive(Debug, Clone)]
-pub struct ChatMessageDisplay {
-    pub role: Role,
-    pub content: String,
-    pub timestamp: i64,
-}