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/app/mode/effort.rs

@@ -16,9 +16,3 @@ pub fn cycle_effort(state: &mut AppStateRest) {
     state.misc.effort_level = (current + 1) % EFFORT_LEVELS.len();
     state.dirty = true;
 }
-
-pub fn set_effort(state: &mut AppStateRest, level: usize) {
-    let clamped = level.min(EFFORT_LEVELS.len() - 1);
-    state.misc.effort_level = clamped;
-    state.dirty = true;
-}