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/runtime/event_loop/mod.rs

@@ -1 +1,2 @@
+#[expect(dead_code)]
 pub mod sessions;

src/app/runtime/event_loop/sessions/deferred.rs

@@ -0,0 +1,16 @@
+use crate::app::state::rest::AppStateRest;
+use crate::app::state::types::ToastKind;
+
+pub struct DeferredOp {
+    pub kind: String,
+    pub handler: Box<dyn FnOnce(&mut AppStateRest) + Send>,
+}
+
+pub fn run_deferred(state: &mut AppStateRest, op: DeferredOp) {
+    let kind = op.kind.clone();
+    (op.handler)(state);
+    state.push_toast(crate::app::state::types::Toast::new(
+        ToastKind::Info,
+        format!("deferred '{}' completed", kind),
+    ));
+}

src/app/runtime/event_loop/sessions/mod.rs

@@ -0,0 +1,27 @@
+use std::path::PathBuf;
+use crate::model::session::Session;
+
+#[expect(dead_code)]
+pub struct SessionManager {
+    pub current_id: String,
+    pub base_dir: PathBuf,
+    pub sessions: Vec<Session>,
+}
+
+impl SessionManager {
+    pub fn new(base_dir: PathBuf) -> Self {
+        SessionManager {
+            current_id: String::new(),
+            base_dir,
+            sessions: Vec::new(),
+        }
+    }
+
+    pub fn load_sessions(&mut self) {
+        self.sessions = Session::list(&self.base_dir);
+    }
+
+    pub fn find_by_id(&self, id: &str) -> Option<&Session> {
+        self.sessions.iter().find(|s| s.id == id)
+    }
+}