Adopt the Word-authored Hyperlink, CommentText and CommentReference style definitions #117

Five styles the library writes by name are not defined in the bundled template, so each site works around the gap:

Today:

>>> document.styles["Hyperlink"]
KeyError: "no style with name 'Hyperlink'"

— on a document where the library itself has just applied that style. The reference resolves to nothing, so Word falls back to default character formatting and the link renders as ordinary text.

#23 has this blocked on having Word available to author the definitions. Three of the five do not need Word. The repo already carries Word-authored definitions of Hyperlink, CommentText and CommentReference, in fixtures Word wrote:

Hyperlink          features/steps/test_files/comments-rich-para.docx
                   features/steps/test_files/par-hlink-frags.docx
                   features/steps/test_files/par-hyperlinks.docx
CommentReference   features/steps/test_files/comments-rich-para.docx
CommentText        features/steps/test_files/comments-rich-para.docx

Those are authentic Word output, not a guess at what Word would write — which is the exact objection that stalled #23.

What to do

1. Lift the three w:style definitions verbatim out of comments-rich-para.docx into src/docx/templates/default.docx and the unpacked default-docx-template/word/styles.xml.
2. Delete _add_default_hyperlink_style() and the branch that calls it (text/paragraph.py:166), and have add_hyperlink() resolve the style through styles like everything else.
3. Leave the comment and footnote sites assigning ids directly for now — that is a separate simplification and the footnote styles are still missing.

FootnoteText, FootnoteReference and the endnote pair are not in the corpus and still need Word, or a Word-authored document from elsewhere. They stay on #23.

Watch out for

• Check w:basedOn on each lifted definition — CommentText is typically based on Normal and CommentReference on Default Paragraph Font. Both exist in the template, but confirm rather than assume, or the imported styles inherit from nothing.
• Hyperlink's definition uses a theme colour (w:color w:themeColor="hyperlink"). It will resolve against the template's own theme, which is the same Office theme the fixtures were written against, so it should look right — but that is worth eyeballing in Word before merging rather than trusting.
• The synthesised style _add_default_hyperlink_style() produces today is hardcoded blue and underlined. The real definition is theme-linked and includes the visited-link behaviour, so links in documents created after this change will look slightly different. That is the point, but it is a visible change and belongs in HISTORY.rst.
• tests/test_reproducible.py and the template part-size assertions move.

Split out of #23 so the unblocked part can ship without waiting for a Word session.