feat: add lesson export and import functionality

- Implemented `LessonExport` and `LessonImport` actions in the action module.
- Added corresponding command parsing for lesson export and import.
- Created functions to handle lesson export and import in the memory module.
- Updated state management to reflect changes after lesson operations.
- Introduced deferred operations for handling asynchronous tasks in the event loop.
- Enhanced the tool execution context to include graduated checks for file operations.
- Added OAuth support with PKCE for secure authorization flows.
- Implemented a loopback server for handling OAuth redirects.
- Refactored various modules to improve code organization and maintainability.

src/app/mode/help.rs

@@ -0,0 +1,38 @@
+use crate::app::runtime::actions::Action;
+use crate::app::state::types::Overlay;
+
+pub const HELP_TEXT: &str = "\
+Keybindings:
+  Ctrl+C    Quit
+  Ctrl+D    Close overlay
+  Ctrl+H    Help
+  Ctrl+P    Settings
+  Ctrl+A    Toggle yolo arm
+  Ctrl+B    Bash panel
+  Ctrl+S    Session hub
+  Ctrl+T    Todo panel
+  Ctrl+W    Workflow panel
+  Ctrl+K    Key input
+  Ctrl+L    Learning dashboard
+  Ctrl+U    Usage dashboard
+  Esc       Close overlay
+  Enter     Submit / confirm
+
+Slash commands:
+  /help             Show this help
+  /quit             Quit session
+  /resume           Resume from overlay
+  /mode <name>      Switch mode (chat, agents, bash, workflow)
+  /lesson <text>    Create a lesson
+  /lesson list      List lessons
+  /lesson export    Export lessons
+  /lesson import    Import lessons
+  /clear            Clear transcript
+  /save             Save session";
+
+pub fn handle_help_action(action: &Action) -> Action {
+    match action {
+        Action::CloseOverlay => Action::CloseOverlay,
+        _ => Action::OpenOverlay(Overlay::Help),
+    }
+}