Save as Web Page wrote only the cell table, so pictures and charts on a sheet
were dropped. A sheet that has either now keeps its own geometry and draws them:
- The table gets the sheet's column widths and row heights (`table-layout:fixed`,
a `<colgroup>`, a height per row); hidden columns and rows take no room and
merged-cell spans count only visible lines.
- A picture is an `<img>` with a `data:` URI, a chart is inline SVG built from
the chart crate's drawing primitives (titles, axes, legends and data labels
included), each absolutely positioned at its anchor cell plus offset.
- Sheets without pictures or charts write byte-identical HTML.
Adds contributors/people.toml entry for bilalmughal.
