fix(docx): write a chart in a table cell as its data table, and draw nothing of it over that table

[DemchaAV]

Why

The DOCX export writes every chart as its data table (writeChartFallback). A chart composed in a
table cell was drawn as well: a composed cell's content has no layout path of its own, its
fragments are among the table's, and drawCellDrawing draws the table's drawings — the chart's
bars and grid lines included. Measured in Word and LibreOffice on Windows, they stood in front of
the data table and hid its numbers ("Sales" read "Sa", 2.5 read "2."), and the chart's axis labels,
the page's text, were not drawn at all. The report said only "exported as its data table".

The log line said "the semantic DOCX export has no layout pass", and ChartNode's and
ChartDefinition's Javadoc, the charts recipe and the Word export example's caption said the same
or that the export "does not draw vector geometry". Neither holds: the export reads the layout and
draws geometry. What it does not write is a Word chart.

What changed

• cellsBuiltFromAChart (in drawCellDrawing): the boxes of a table's cells whose drawing is
  a chart's alone (chartDrawnAlone — one chart, and beside it only paragraphs, lists, spacers,
  page breaks, alignments and sections or containers that paint nothing), every box the layout
  placed the cell in (a repeated header row has one a page). A table fragment those boxes hold
  (CellBox.holds) is not drawn; one that only reaches into them is. The chart is recorded in
  chartsNotDrawn, reset per export.
• The chart's note: a chart composed in a cell that the export does not find drawing alone —
  beside other drawings, which it cannot tell its own from, or in a table composed in a cell, whose
  cells the layout gives no box — adds "its bars, lines and slices are drawn as well, where the page
  draws them, over the table and without its text".
• The log line, writeChartFallback's Javadoc, ChartNode and ChartDefinition (core, Javadoc
  only), docs/recipes/charts.md, docs/recipes/docx-export.md, and WordExportExample's caption
  now say the export writes no Word chart; assets/readme/examples/word-export-companion.{docx,pdf}
  are re-rendered for the caption (CommittedAssetDriftTest named exactly those two).
• CHANGELOG v2.5.0.

A drawing another cell pushes wholly into a chart's box — by a layer's offset or a margin below
zero — is taken for the chart's; the Javadoc says so.

Verification

• Before → after, Word on Windows, a chart alone in a 300pt cell: bars and grid lines over a
  clipped data table → the data table alone.
• ./mvnw -B -ntp test -f render-docx/pom.xml — DocxChartInACellTest (new, 9, each with-layout
  case asserting the layout stood behind it): a chart a cell is built from — its data table there,
  no drawing, the plain note, no "cell drawing" note; in an unpainted section, alone and under a
  caption, not drawn; beside a disc in its cell, drawn and named; two charts in a cell and a chart
  in a painted section, drawn and named; a neighbour's tile in its own cell, and one a margin below
  zero widens into the chart's cell, still drawn; a chart in a header row repeated over pages, and
  in a cell spanning two columns, drawn on no page; in a table composed in a cell, drawn and named;
  in the flow and with no layout, the plain note; one backend over two exports of one chart node.
• 11 sabotages, each undoing one part — the skip, the record, the clause both ways, the reset, the
  drawing-alone walk, holds for overlaps, the first box only, the cell's own content only, two
  charts taken for one, a painted wrapper taken for nothing — all caught.
• Corpus: 62/62 DOCX byte-identical; report notes 1246 → 1246.
• ./mvnw -B -ntp clean verify — BUILD SUCCESS (core 821, render-docx 1755, examples 93, qa 1820); CommittedAssetDriftTest
  passes on the re-rendered example; the knowledge pack's --check and claims pass.

Lane: render-docx (semantic backend) — cell drawings and a report note; core Javadoc and the
example's caption.