feat: set up Flutter project with drift database, Riverpod providers, and LLM service layer

- Configure dependencies: drift 2.32.x, flutter_riverpod 3.3.1, fl_chart 1.2.x,
  flutter_local_notifications 21.x, local_auth 3.x, and supporting packages
- Drop riverpod_generator (incompatible analyzer version with drift_dev 2.32.x);
  convert all providers to manual Riverpod 3.x API using Notifier<T> and typed families
- Define drift schema: MoodEntries, Activities, EntryActivities, Tags, EntryTags,
  LlmInsights, UserSettings with four DAOs (mood, activity, insight, settings)
- Add LLM service abstraction (LlmService) and MediaPipe implementation
- Fix SettingsDao.delete → deleteByKey to avoid shadowing drift's inherited delete method

windows/runner/flutter_window.h

@@ -0,0 +1,33 @@
+#ifndef RUNNER_FLUTTER_WINDOW_H_
+#define RUNNER_FLUTTER_WINDOW_H_
+
+#include <flutter/dart_project.h>
+#include <flutter/flutter_view_controller.h>
+
+#include <memory>
+
+#include "win32_window.h"
+
+// A window that does nothing but host a Flutter view.
+class FlutterWindow : public Win32Window {
+ public:
+  // Creates a new FlutterWindow hosting a Flutter view running |project|.
+  explicit FlutterWindow(const flutter::DartProject& project);
+  virtual ~FlutterWindow();
+
+ protected:
+  // Win32Window:
+  bool OnCreate() override;
+  void OnDestroy() override;
+  LRESULT MessageHandler(HWND window, UINT const message, WPARAM const wparam,
+                         LPARAM const lparam) noexcept override;
+
+ private:
+  // The project to run.
+  flutter::DartProject project_;
+
+  // The Flutter instance hosted by this window.
+  std::unique_ptr<flutter::FlutterViewController> flutter_controller_;
+};
+
+#endif  // RUNNER_FLUTTER_WINDOW_H_