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/onboard_provider.rs

@@ -0,0 +1,20 @@
+use crate::model::settings::Settings;
+
+pub const PROVIDERS: &[&str] = &["OpenRouter", "Anthropic", "OpenAI"];
+
+pub fn set_provider(settings: &mut Settings, provider: &str) {
+    settings.provider = match provider {
+        "OpenRouter" => "openrouter".to_string(),
+        "Anthropic" => "anthropic".to_string(),
+        "OpenAI" => "openai".to_string(),
+        _ => "openrouter".to_string(),
+    };
+}
+
+pub fn set_api_key(settings: &mut Settings, key: String) {
+    settings.api_key = Some(key);
+}
+
+pub fn set_model(settings: &mut Settings, model: String) {
+    settings.model = model;
+}