feat(pptx): table rows — fills, borders, and cell text at graph coordinates

[DemchaAV]

Why

The fixed PPTX backend renders text and vector shapes but throws UnsupportedNodeCapabilityException on table rows — the biggest remaining gap for real documents. Native PowerPoint tables cannot hold the engine's geometry (they re-lay-out their content), so tables need the same positioned-shapes treatment the rest of the backend uses.

What changed

• PptxTableRowFragmentRenderHandler: each TableResolvedCell renders as a positioned fill rectangle, butt-capped border edge lines, and per-line text frames. Border math mirrors the PDF handler exactly: horizontal lines extend half a stroke width past internal joins (adjacent cells' perpendicular borders otherwise leave a corner notch after rasterization) while outer table edges stay clamped; a fragment that starts a page forces its TOP border; row-spanning cells grow downward through merged rows via their negative yOffset.
• Two-pass paint discipline: PptxFixedLayoutBackend.renderGraph groups contiguous same-path row fragments and calls renderFills for every row before any renderBordersAndText — the port of PdfFixedLayoutBackend.renderTableRowGroup, so cell fills always land beneath strokes across row-span joins.
• Cell text mirrors the PDF handler line for line: control-sanitized lines measured with PdfFont.getTextWidth, nine-way anchored inside the padded cell box, drawn through sanitizeForRender into per-line frames seated at baseline − viewer ascent.
• The frame discipline (wrap off, autofit off, zero insets, LEFT align, kern=0) moved into a shared package helper PptxTextFrames; the paragraph handler now delegates to it — one home for the rules both text paths must agree on, no behavior change (setShapeName additionally learned connector shapes, which previously went unnamed).
• Capability matrix: table-row cell flips to supported with the implementing classes; CHANGELOG entries regrouped so backend capabilities sit under Public API and the test inventory under Tests.

Verification

./mvnw -B -ntp clean verify (full 10-module reactor gate) → BUILD SUCCESS; render-pptx suite grows 29 → 32 tests.

• PptxTableGeometryTest — re-derives every fill rectangle, border segment (including caps and the page-start TOP), and text frame from the captured LayoutGraph and matches them against the reopened .pptx across a page break with a repeated header; pins that the row-spanning cell actually resolved (yOffset < 0 asserted), that a page-start fragment exists, and the fills-before-ink paint order per slide. A synthetic-fragment test pins the page-start TOP-border branch at the handler level, independent of what border sides the engine emits.
• PptxTableParityDemoTest — writes the reviewable pair tables.pdf / tables.pptx + per-page PNGs under render-pptx/target/visual-tests/pptx-parity/tables/; the previews match including the zebra fills, the merged "Fixed layout" cell, and the repeated header on page 2.

Notes

• TableResolvedCell.fillInsets is unused by both backends today — parity preserved, not a new gap.
• The demo's table is one table per page; the geometry test's fills-before-ink assertion is scoped per slide, which is stricter than the per-group guarantee and would need loosening if a fixture ever placed two tables on one slide.

Lane: canonical (document.backend.fixed.pptx) — backend surface; engine, layout, and the PDF paint path untouched.