Add a "horizontal stretch" option/button to wide tables in responses to stretch their width to fill the viewport, beyond the width of the rest of the response

[munael]

It would be helpful to be able to expand a table in responses to fill the thread view horizontally. Similar to Notion's feature for stretching a table to fill the viewport width regardless of the selected width of the article.

See also: #10769
for controlling the whole response thread's width.

[Vantrongs]

What I'd like: open the table in an overlay that uses the whole window, the way images already expand (ZoomableImage). Chat width → Wide or Full (#11594) doesn't cover this. It widens every message, and long prose is harder to read in a wide column, while a table is easier to read when all of it is visible at once. Only tables need the extra width.

Today the button on a table is "Expand table cells" (MarkdownTable in ChatMarkdown.tsx). Its Maximize icon suggests a larger view, but it only turns off cell wrapping: the table grows taller and still scrolls sideways inside the chat column.

A small addition for long tables, in the overlay or inline: when hovering a cell, highlight its column header and its row's first cell, like the row and column headers in a spreadsheet. Then it's clear which row and column a value belongs to without tracing across the table.

[kumibrr]

Having a ctrl+scrollwheel is good enough