Blog tables are readable in dark mode again

Blog tables are readable in dark mode again. On 19 posts they rendered as
empty rows: the text stayed pure black while the page behind it went black.

Not the table CSS, which uses theme tokens and inverts correctly. The colours
arrived with the content. Those tables were pasted out of Google Docs, which
writes color:#000000 onto every run of text, and an inline style outranks the
stylesheet — so the black survived into dark mode. About 1,500 pieces of text
were pinned that way, plus ~190 to the Google Docs link blue. A few cells were
pinned to white, the same bug facing the other way, unreadable in light mode.

The fix drops color and background-color from pasted styles where a post is
prepared, alongside stripEmoji and liftHeaderNotes, rather than as an
!important override fighting the paste from the stylesheet. Text now inherits
the site's own colours and follows the theme like everything else, and a writer
can keep pasting from Google Docs without it breaking again.

The paste's font and size are deliberately left alone. They are wrong in their
own way but they are legible, and removing them would redraw twenty posts in
both themes rather than fix the one thing that was broken.

Verified on staging across all 21 affected posts: 855 pinned colours before the
deploy, 0 after, with all 76 tables intact. On the worst post, 221 text nodes
measured in each theme and none below WCAG AA.

Found on the way: blog posts 500 on every Vercel preview deployment, which is
why this was verified locally and on staging rather than on the PR preview.
That is pre-existing and unrelated to this change; tracked in WEB3-3.