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/view/theme.rs

@@ -4,7 +4,6 @@ pub struct Theme;
 
 impl Theme {
     pub const PRIMARY: Color = Color::Cyan;
-    pub const SECONDARY: Color = Color::Magenta;
     pub const SUCCESS: Color = Color::Green;
     pub const WARNING: Color = Color::Yellow;
     pub const ERROR: Color = Color::Red;