Fix How-To guide titles in Antora - #194

The How-To index displays .adoc filenames instead of guide titles because the generated Antora pages lack document headers.

Add the attribute used by the documentation generator to promote each guide's heading for Antora while preserving its chapter level in the PDF.

Validation:

• Build the documentation and its reactor dependencies with the man-pages profile.
• Verify that all 13 generated Antora pages have document titles and that the PDF table of contents retains the guide headings.
• Run the How-To link checker and its Python tests.