Introduces `DownloadManager` and `DownloadService` to handle module
downloads as foreground services. This ensures downloads are not
interrupted by the system and provides real-time progress updates via
system notifications.

Key changes:
- Added `DownloadManager` to track download states and callbacks.
- Added `DownloadService` with support for progress notifications,
  cancellation, and post-download installation actions.
- Integrated download progress and status into `ModuleScreen`,
  `ModuleRepoMaterial`, and `ModuleRepoMiuix`.
- Added deep link resolution for the "Install" action in notifications.
- Added necessary permissions (`FOREGROUND_SERVICE`, `POST_NOTIFICATIONS`)
  and service declaration to `AndroidManifest.xml`.
- Updated UI to distinguish between "Download" and "Install" states.

* Made with Claude