fix(docx): set what follows a panel where the page does, and name the rest

[DemchaAV]

Why

Word sets a panel's content below its whole top border and its margin, and ends the row its
margin and its whole bottom border past the content; the page strokes each border on the
panel's edge, taking no room. With the cell margin written as padding − border/2, a panel
reaches past the page's box by border/2 + max(0, border/2 − padding) on each edge — measured
in Word 16 and LibreOffice on Windows alike on a 2pt border: 2pt with no padding, 1pt with 1, 2
or 4pt of it. The export took each border whole out of the space round the panel, so a padded
card with a gap below it stood what followed half a border high, unnamed, and only a row's panel
named the rest.

What changed

All in DocxSemanticBackend:

• outsideTheRow states the measured reach. writePanelPiece takes it out of the space
  round the panel first (the border stands where the page strokes it), then out of the panel's
  padding (takeOffTheCellMargin — the border drawn that much inside the panel's edge, the
  content where the page sets it), then, above, out of the room over the first line
  (takeTheTopBorderInside). What none of them takes is named: on the panel's node kind for its
  top border, on the block below for its bottom one.
• What stands a block lower is named on it (nameTheTailNotTaken, subject space above, one
  note with the total): a panel's bottom border reach, a line hanging below the block above, the
  0.1pt paragraph Word keeps between two tables, and a pull — a negative bottom margin, a
  panel's as a paragraph's — that neither the space below it nor the next block's own top edge
  gives back (Word sets no block over another). The bottom reach the space below does not take
  comes out of that panel's padding first (borderBelowCell).
• A cell no longer carries the border of the card ending it into the flow (carriedBorder):
  its writer decides. A row takes it, with the cell's hanging line, out of the room under that
  cell, then the card's padding; a panel takes it out of the card's padding, then its own; a
  table's composed cell or a column of side-by-side layers — whose content the layout does not
  measure against its row — takes it out of the card's padding and names the rest on the cell's
  content, up to that much where a cell beside it may hold it.
• holdThePanelsHeight: Word and LibreOffice read a panel's written row height as its
  content's, with its margins and both borders round it (measured: held a point above its
  content, an outlined card stood a point taller). A panel holds the page's height less its
  padding, as a uniformly ruled card already was, and less what the room over its first line gave
  its top border, which used to come off it a second time; a shape container, its layers centred
  in it, holds its outline's height less both borders and its margins (it was held one border
  less only), and nothing of its borders reaches past it.
• A panel's last line hanging past its content comes out of its padding below, then the space
  under it. A container's top edge above a table counts as room for the table's tail. A panel the
  layout moves to a new page leaves the tail above on its page and holds the space above it there,
  as a table does. A tail or pull left over a block that takes nothing out of a top edge of its
  own — a list item — is named at the next block or at the section's end.

Docs: the recipe's "What a panel keeps and loses" (borders, height, what hangs below, the
measured nesting) and its pull paragraph, the capability matrix's rectangle row, render-docx/ README.md, the field ledger (DocxNodeFieldLedgerTest: panels' stroke/borders and
paragraphs' and panels' margin/padding name what is reported), and four unreleased v2.5.0
CHANGELOG entries that described the old border model (row paint, CobaltRota's chips,
MerchantInvoice, the badge entry).

Verification

• ./mvnw -B -ntp clean verify on this branch with fix(docx): write a page zone's picture in its line, and stand each part on its own baseline #872 merged → BUILD SUCCESS: render-docx
  1307 run, 0 failures, 1 skipped, qa 1820, core 818.
• New DocxPanelTailTest (40): borders above and below with and without padding and space, the
  space before the padding, held heights, shape containers, hangs, cards ending a panel, a row's
  cell, a table's cell (alone and beside another) and a column of layers, pulls before a
  paragraph, a spacer, a table and a list, a pull against a card's top border, a panel moved to a
  new page, touching tables and cards named once with the total. Exact values updated in
  DocxContainerSpacingTest, DocxPanelHeightTest, DocxRowPaintTest.
• 32 sabotages of the rules above, each caught by at least one test.
• A probe of cards with 2pt borders above, below and all round (padding 0/1/4, with and without
  space round them), cards outlined at 0.5 and 2pt stacked and at 0.5pt in a row's columns, and
  chips in table cells, converted by Word 16 and LibreOffice on Windows: every line stands where
  the page sets it, or as much lower as the report names — within 0.15pt in Word and 0.05pt in
  LibreOffice.
• DOCX fidelity corpus: 25 of 62 documents change; the report names 15 more notes (14 × the 0.1pt
  between two tables; ObsidianInvoice's totals row, 0.72pt = a 0.62pt border + that 0.1pt). Word
  baseline (word-windows*.tsv, via scripts/docx-visual/word-fidelity.ps1 -Update): 12
  documents nearer the page (letter-engineering_resume median 1.27 → 0.13pt,
  cv-engineering_resume 0.58 → 0.24, proposal-modern 0.48 → 0.19, cv-minimal_underlined
  0.71 → 0.44), 8 further (cv-panel 0.34 → 0.83, invoice-subscription 0.23 → 0.61,
  cv-modern_professional 0.09 → 0.32, cv-classic_serif 0.17 → 0.31, four by under 0.2pt).
  LibreOffice on Windows likewise, 13 nearer and 9 further. LibreOffice on Linux
  (libreoffice-linux*.tsv, from CI's docx-fidelity artifact): 24 documents change, 11 nearer
  in median (letter-engineering_resume 1.40 → 0.19pt, invoice-obsidian 1.38 → 0.27pt with 15
  lines over 2pt where there were 25), 9 further — the same documents as on Windows.

Notes for review

Where traced, the documents that move further from the page do so because the whole border taken
out of the space had been making up for errors elsewhere, now exposed: a heading's baseline left
up to half a point from where Word seats it in an exact line (cv-modern_professional's summary
heading stands where the layout sets it, 82.57 against 82.55pt, its baseline 0.36pt lower), a
spacer of no height written as a 0.1pt paragraph (one per card in cv-panel), rounding to the
twip inside a card, a 0.37pt step between a table's header and its first row
(invoice-subscription), and the space above a block moved to a new page written at the page's
top (proposal-editorial). cv-charcoal_gold, cv-nordic_clean and invoice-workspace move by
under 0.06pt in median, not traced. Each traced cause is a defect of its own, outside this change.

Lane: shared-engine (DOCX backend) — render-docx only, no public API.

Merge order: follows #872, merged into this branch; the two touch disjoint parts of the
backend (page zones there, panels here), and no corpus document has a page zone.