feat(ui): mark replies with a thread line, a tint and dimmer text

Indentation alone still read as a table, which was the user's original
complaint about the whole item. Three cues now say the rows belong to the
thread above them: a spine down the left of the expanded block with a stub out
to each reply, a background tint, and text a size down and undimmed only when
unread.

Both colours are mixed from the palette rather than fixed, the same rule
readColour follows: a tint that reads as grouping on a light theme is invisible
or muddy on a dark one. The tint is deliberately near the threshold of noticing,
since it sits beside the deleted and spam fills, which carry real meaning and
must stay the loudest thing in the list.

The spine is accumulated across the visible reply rows and drawn once after the
loop. Drawn per row it left a gap at every row boundary and read as a column of
dashes rather than as the structure holding the block together.

Two bugs fixed here, both mine, both from the previous commit:

Clicking the expander did nothing. setRootIsDecorated(false), needed to stop
the style painting its own indicator under ours, also removed the style's hit
area, so the glyph rendered perfectly and was inert. ThreadListView handles the
press itself now, over the strip the delegate reserves, leaving the rest of the
subject cell to select the row.

Every click then expanded rather than toggling, because isExpanded and
setExpanded are keyed on column 0 and were being asked about the subject-column
index, which always answers false.

Visible, clickable and toggling are three separate properties and a test for
one passes against the other two being broken: the pixel test proved the
triangle was drawn while it could not be clicked, and the first click test
proved it opened while it could never close. The test now clicks twice and
asserts open then closed.

replyRowsKeepTheirTextUnderTheThreadLine covers the other trap. paintEvent runs
AFTER the cells, so the first version of the tint filled the whole reply row and
erased the sender and subject the delegate had just drawn: zero surviving text
pixels, a block of blank tinted rows. The fill and the stub stay in the band
below the text, where the tag strip lives on thread rows.

0 files changed, 0 insertions, 0 deletions