feat: Implement lesson generation feature and update status display

- Added functionality to generate lessons based on code reviews, including prompts and instructions for the reviewer.
- Updated the `.gitignore` to exclude lesson documentation files.
- Removed the `/lesson` command from the help menu and command parsing.
- Enhanced the status bar to display a message when a lesson is being generated.
- Introduced a new `lesson_running` state to track lesson generation progress.
- Updated various components to handle the new lesson generation workflow, including subagent events and token usage tracking.

src/app/runtime/commands.rs

@@ -21,9 +21,6 @@ pub fn apply_command(command: Command) -> Vec<Action> {
         Command::Quit => {
             vec![Action::QuitConfirm]
         }
-        Command::LessonInteractive => {
-            vec![Action::OpenOverlay(Overlay::Learning)]
-        }
         Command::McpOpen => {
             vec![Action::OpenOverlay(Overlay::Mcp)]
         }