0.8.2 — a thread is named in its author's own words

Migrations: none. Presentation only; no published document changes.

A thread is named in its author's own words. A thread's content_html
contains other people's writing, baked in as transclusion blockquotes. That is
right on the thread's own page, where a quote is shown as a quote with a
provenance line under it. It was wrong everywhere the client had to name the
thread in one line, because flattening that HTML to text drops the structure
that made the attribution legible.

Measured on a live node before the fix: of 19 published threads, 5 opened
with a transclusion — which is the shape the stub action prefills, so it is
the common case. For those five, the browser tab, the search-result heading,
the social card, the RSS headline and the feed-page excerpt were all someone
else's sentence presented as the author's. Others ran the author's prose
straight into a quote mid-excerpt with no boundary, so a card read as one
continuous paragraph by one person when it was two people.

Fixed in one place and used by all four surfaces: the feed card, the page
<title>/og:title/description, the RSS headline and the archive row. A
thread's card also gained a quote count (⧉2), which is what now says the
item is longer than the teaser; and a thread that quotes without adding
anything of its own names what it answers instead of borrowing the quoted
sentence.

Nothing here changes the wire. content_html, the item document, the feed
description and the static export all keep the quotes, and the thread's own
page still renders them in full with their provenance.

Also fixed: a thread mixing whole and partial transclusions mis-paired its
provenance lines, because the injector matched the class attribute as a literal
string — so a partial quote got no line and every following line shifted onto
the wrong quote.