Same class as the XLSX rPh fix: a phonetic guide annotates the base text and
is not part of it. `_extract_docx` collected every w:t in the paragraph, so a
ruby-annotated run rendered as guide + base ("トウキョウ東京"). Skip the w:rt
subtree; w:rubyBase stays. The phonetic test now covers XLSX shared/inline/rich
and DOCX ruby through the registered read_file handler.