fix(docx): break a table across pages where the layout breaks it

[DemchaAV]

Why

Word re-paginates a DOCX itself, so it only breaks a table where the layout does if the file says where. The layout:

• splits a table only between rows. A row that does not fit what is left of a page moves to the next page whole.
• repeats the first repeatHeader(n) rows at the top of every page the table continues on.
• never leaves those header rows at the foot of a page with no body row under them (splitTable refuses a head that is only header).

The export wrote none of it. Word's default lets a row break mid-line wherever its own page ends, and a long table printed its header once.

What changed

• DocxSemanticBackend.breakRowsWhereTheLayoutDoes, run after each table is written:
  • Every row the layout placed gets w:cantSplit.
  • The first repeatedHeaderRowCount rows get w:tblHeader, and their cell paragraphs get w:keepNext, so the last header row stays on the page of the first body row.
  • A table that is all header gets no keep-with-next: with no body row under it, that would tie the table to whatever paragraph follows.
• writeRow keeps a row of blocks whole the same way. RowDefinition lays a row out as one atomic piece.
• Rows are gated on the layout having placed them, not on a height check. The layout refuses a row taller than the page (AtomicNodeTooLargeException), and the session then exports without a layout. So a placed row is always one a page can hold. In a document that could not be laid out, rows stay free to break, because no page holds such a row whole.
• DocxLayoutMetrics:
  • placedRow(table, row) and placed(node) are new.
  • The "rows that span this table" filter moved out of tableColumns into ownRows, so both callers skip a composed cell's nested table. That table emits its rows under the owner's path.
• Recipe table rows, capability-matrix DOCX table cell, and a CHANGELOG entry under v2.5.0.
• assets/readme/examples/word-export-companion.docx is re-rendered. Its document.xml diff is exactly six <w:trPr><w:cantSplit/></w:trPr> additions, one per table row, and nothing else.

Verification

Full reactor gate (clean verify over core, render-pdf/docx/pptx, templates, testing, qa, coverage) → BUILD SUCCESS. Examples after install: 93 green; CommittedAssetDriftTest went red on the stale preview until it was re-rendered.

New DocxTablePaginationTest (7 tests):

• Placed rows are cantSplit.
• repeatHeader(2): both header rows are tblHeader and keep with the next row, and the body rows are neither.
• No repeatHeader: no header row and no keep.
• An all-header table keeps no keep-with-next.
• A table with a row too tall to lay out has no cantSplit row.
• A bare export without a layout has no cantSplit but still gets tblHeader.
• addRow is kept whole.

Sabotaging both guards (placedRow → true, header keep → always) fails 3 of them.

Lane: shared-engine (render-docx) — table row properties only; no public API change.