fix(docx): make a block's anchor a bookmark Word can link to

[DemchaAV]

Why

anchor(...) sits on a paragraph, a section, a container, a table or an image, and linkTo(...) jumps to it. The DOCX export wrote a Word bookmark only for a paragraph's anchor. An anchor on any other block was dropped. The link to it was still written, with w:anchor naming a bookmark that did not exist, so in Word it went nowhere.

This is also the precondition for page references. A PAGEREF field to a block's anchor has to find a bookmark, or Word shows "Error! Bookmark not defined." when the field updates.

What changed

• DocxSemanticBackend.writeNode now wraps a block's output in a bookmark named after its anchor (bookmarkAround). This covers a section, a container, a table and an image. It goes through the same DocxBookmarkNames as paragraph anchors, so the name a link uses is the name the bookmark carries. It sits alongside the existing keep-together pass.
  • The bookmark opens before the first word of the block's first paragraph. A block that starts with a table opens in the table's first cell.
    • addNewBookmarkStart appends after the runs, so the element is moved with an XmlCursor to just after the paragraph's w:pPr.
    • Left where it was appended, a link would land after the first line's text instead of on it.
  • It closes after the block's last paragraph, or in the last cell when the block ends with a table.
  • A block that wrote nothing gets no bookmark. That covers an empty section, and an anchor on a node this export drops, such as a shape.
• A paragraph's own anchor is unchanged. The paragraph writer still wraps its own text.
• Docs updated:
  • the recipe's links-and-anchors row;
  • the capability-matrix internal-links row, whose DOCX cell said ❌ although internal links have been written since feat(docx): export a link as a link, and an anchor as a bookmark #707;
  • CHANGELOG under v2.5.0.

Verification

In an editor. A document with a link on page 1 to a section anchor on page 2, converted with LibreOffice: the link's destination is page 2, where the section starts.

Gate. Full reactor gate (clean verify over core, render-pdf/docx/pptx, templates, testing, qa, coverage) → BUILD SUCCESS. Examples after install: 93 green. No committed preview moved.

New DocxBlockAnchorTest (4):

• a section's anchor opens before the first run of its first paragraph, and a link's w:anchor names it;
• the bookmark closes on the section's last paragraph with the same id;
• a table's anchor opens in its first cell and closes in its last;
• an image's anchor marks the picture's paragraph;
• an anchored section that writes nothing leaves no bookmark.

Removing the move to the paragraph start fails the section test.

Lane: shared-engine (render-docx). No public API change.