add javadocs for internal classes

- for cross-project development and debugging, include the option of generating javadocs for internal classes
- standardize and clean-up docs to markdown/html format

No file, test, or entry point is named. Start by inspecting the repository documentation and build configuration to determine how internal-class Javadocs are generated and which docs need Markdown or HTML cleanup. Done means the generation option is available and the documentation format scope is consistently addressed.

Written by the indexing model from the issue text.