Replaced ISiteProcessor interface with Command abstract class.
Refactored SourceFileProcessor to CollectSourceFile command.
- Introduced PageCommand to serve as a base class for commands that process individual pages. This abstract class replaces the IPageProcessor interface.
- Changed MarkdownProcessor to inherit from PageCommand and renamed it to TransformMarkdownPage.
- Changed RazorProcessor to inherit from PageCommand and renamed it to TransformRazorPage.
- Renamed CollectSourceFiles command to CollectSiteFiles so that the word Site is present in its name.