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.

Cargo.toml

@@ -36,6 +36,7 @@ rmcp = { version = "1.8", default-features = false, features = ["client", "trans
 chrono = { version = "0.4", features = ["serde"] }
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+webbrowser = "1"
 
 [[bin]]
 name = "zesdex"