feat(pptx): import table styles, live charts, and EMF/WMF fallbacks

[karthikmudunuri]

Summary

Implements the round-2 plan from #38. Three deferred items from #36 land together so real-world client decks stop dropping recognisable content on import.

Closes the implementation half of #38.

1. Table styles

• Parse ppt/tableStyles.xml once per deck (resolved via presentation.xml.rels), honour file-level <a:tblStyleLst def=\"…\"> default.
• Resolve <a:tblPr><a:tableStyleId> and apply the matching style's parts (wholeTbl / firstRow / lastRow / firstCol / lastCol / band1H / band2H).
• <a:tblPr> flags (firstRow, firstCol, lastRow, lastCol, bandRow) decide which parts apply; cell-level <a:tcPr><a:solidFill> still wins as an override.
• TableElement gains rowAltFill, firstColFill, lastColFill, lastRowFill, hasHeader, bandRows, and per-region text-colour overrides; the renderer applies them in PPTX-faithful precedence.

2. Charts — cached image + live rendering

• <p:graphicFrame> with <c:chart> first tries the chart part's cached raster preview (ppt/charts/_rels/chartN.xml.rels → …/image) and emits an ImageElement.
• When no cached preview ships, the chart XML is parsed into a new ChartElement (bar / column / line / area / pie / doughnut, with standard / stacked / percentStacked grouping, series fills, value labels, number-format codes, optional title) and rendered live via a lazy-loaded Apache ECharts import.
• Series colours: explicit <c:spPr><a:solidFill> wins; otherwise PowerPoint's default-palette cycle theme.accent{(c:idx % 6) + 1} is used.
• The source <p:graphicFrame> OOXML is preserved on the element so save round-trips re-emit the source chart part verbatim (including its embedded xlsx workbook).
• setOption(option, true) + explicit per-series itemStyle.color so palette merging can't drop colours when multiple series share a name.

3. EMF / WMF — raster fallback + Canvas decode

• When a <p:pic> references EMF/WMF, the importer first looks for a renderable sibling: alt blip in <a:extLst>, extra rels entry on the picture, or same-basename PNG/JPEG/SVG in the slide rels.
• When no sibling exists, the metafile is decoded in-browser via emf-converter (Canvas-based EMF/WMF replayer) and rendered as PNG. The Dickinson sample wordmark (EMF-only) now appears instead of dropping.
• Headless environments without Canvas / OffscreenCanvas (SSR, Node) gracefully fall back to the legacy diagnostic-skip — never throws.

Bonus: tint / shade fix

<a:tint val=\"20000\"/> and <a:shade> modifiers now operate per-RGB-channel per ECMA-376 §20.1.2.3 (mix with white / black respectively) instead of as an HSL-luminance shift. This was silently over-saturating the pastel Office accent palette — most visible on table-style band rows like "Medium Style 2 – Accent 1" where accent1 @ tint 20% should be #F2CCCC (light pink), not the saturated red the old code produced.

What's still out of scope

• Live editing of chart data inside Slidewise (we re-emit the source chart XML verbatim on save).
• Embedded TTCOMPRESSED fonts, animations, SmartArt — explicit non-goals.

Dependencies

• emf-converter ^1.1.6 (MIT, 0 deps, ~310 KB unpacked) — Canvas-based EMF/WMF decoder.
• echarts ^6.0.0 — lazy-loaded only when a deck actually contains a ChartElement.

Test plan

• pnpm tsc --noEmit -p tsconfig.lib.json clean.
• pnpm vitest run — 35/35 passing (4 new fixtures in round2.test.ts cover table styles, cached chart, EMF raster sibling, EMF-only skip).
• Manual: imported Dickinson_Sample_Slides.pptx, eyeballed:
  • slide 2 — Dickinson wordmark (EMF) renders via in-browser decode.
  • slide 4 — stacked column chart renders with the gray + red theme-accent colours.
  • slide 5 — "Medium Style 2 – Accent 1" table renders with the correct header / banded-row pinks.

Bundle impact

• emf-converter: ~310 KB shipped only when a deck triggers the EMF fallback (dynamic import()).
• echarts: lazy-loaded on first ChartElement render — zero impact for chart-free decks.