feat: Enhance EpisodeItem and Player components with loading states and improved playback controls

- Added `isLoading` prop to `EpisodeItem` for loading state management.
- Implemented loading spinner in the play button of `EpisodeItem`.
- Added completed state indicator in `EpisodeItem`.
- Refactored `Player` component to handle buffering states and keyboard shortcuts for playback control.
- Introduced playback configuration in `APP_CONFIG` for customizable shortcuts and increments.
- Enhanced error handling in `rssService` with detailed diagnostics.
- Added new `AppError` type for structured error reporting.
- Created `version.json` for version tracking.

Author: macintorsten