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/tool.rs

@@ -15,14 +15,6 @@ pub struct ToolFunction {
     pub arguments: Value,
 }
 
-#[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct ToolResult {
-    pub tool_call_id: String,
-    pub output: String,
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub is_error: Option<bool>,
-}
-
 pub fn sanitize_tool_arguments(args: &Value) -> Value {
     match args {
         Value::String(s) => {