fix(read): repaint the card when one message is marked read

Follows the message-scoped mark-read. The user reported the write going
out with nothing visible changing: the status bar counted an unsynced
edit while the card stayed bold and the message pane still showed the
`unread` tag, until the next query corrected it.

sendMessageTagChange made no optimistic model update on purpose, because
applyTagChange is keyed by THREAD and repainting a whole row for a
one-message edit would claim every reply had changed too. That trade is
right for an explicit tag edit and wrong for auto mark-read, where the
visible change IS the feature and the delay exists to deliver it.

ThreadListModel::applyMessageTagChange updates the message wherever it
is held, as a child row and as `first`, and lets the thread's summary
follow only when the answer is unambiguous: a thread reads as unread
while ANY message does, so the tag is cleared from the thread only when
no other message still carries it. For an unexpanded multi-message
thread the per-message tags are not loaded, so the summary is left for
the next query rather than guessed at.

Mutation checked: without the call the card holds `unread` for the full
timeout.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions