feat: add todo management feature; implement todo content tracking and display in the UI

src/app/runtime/actions/mod.rs

@@ -303,6 +303,20 @@ pub fn apply_action(state: &mut AppStateRest, action: Action) {
             state.misc.tick_count = state.misc.tick_count.wrapping_add(1);
             let now_ms = chrono::Utc::now().timestamp_millis();
             state.misc.drain_expired_toasts(now_ms);
+
+            if state.misc.tick_count.is_multiple_of(10) {
+                let todo_path = state.session_dir.join("todo.md");
+                if let Ok(content) = std::fs::read_to_string(&todo_path) {
+                    if content != state.misc.todo_content {
+                        state.misc.todo_content = content;
+                        state.dirty = true;
+                    }
+                } else if !state.misc.todo_content.is_empty() {
+                    state.misc.todo_content.clear();
+                    state.dirty = true;
+                }
+            }
+
             // Background API connectivity check — runs on a background thread
             // every ~1s while disconnected, every ~30s while connected, so the
             // status bar reflects real API availability without user input.