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/stream/turn.rs

@@ -16,7 +16,7 @@ use serde_json::Value;
 /// sequence), remove it; if inside a string, append `"`; then close
 /// every unclosed opener in reverse (LIFO) order.
 ///
-/// Why: LLM responses can be cut off (max_tokens, network) mid‑JSON
+/// Why: LLM responses can be cut off (`max_tokens`, network) mid‑JSON
 /// string, but we want tools to receive whatever arguments were already
 /// emitted so the partial work can proceed.
 ///