Refactor Lite to use Frontend Package and Migrate to Riverpod

[Yuyu-1115]

Again, this is a extremely rough WIP to streamline development

---

This pull request removes a large amount of code related to the course selection feature, including repositories, storage, URL sharing, and theme management. The changes appear to be a major cleanup or deprecation of the course selection data layer and supporting utilities, as well as the removal of custom widgets and theming code. Additionally, it removes configuration for platform-specific implementations and related imports.

The most important changes are:

Removal of Course Selection Data Layer

• Deleted all code for course repository, schedule repository, and related data models, including course_repository.dart, course_schedule_repository.dart, course_schedule_catalog.dart, and all associated DTO mappers and static/mock data. [1] [2] [3]
• Removed course selection storage abstraction and platform-specific implementations, including in-memory and web storage, as well as the conditional export logic. [1] [2] [3] [4]

Removal of Course Sharing Utilities

• Removed all code for encoding/decoding share codes, building share URLs, and cleaning share codes from URLs, including platform-specific implementations and conditional exports. [1] [2] [3] [4] [5] [6]

Removal of Custom Widgets and Theming

• Deleted the custom OwnedChangeNotifierBuilder widget and all related typedefs.
• Removed the AppTheme and AppThemeController classes, which provided application theming logic.

Project Configuration Updates

• Updated .gitignore to exclude pubspec_overrides.yaml for local dependency overrides.
• Added the riverpod_lint analyzer plugin to analysis_options.yaml for improved linting.