Draw a background task's command as code, and frame the card it opens

A backgrounded command in a session's panel was a terminal glyph beside its
words. The glyph said "command" and so did the monospace face, which is the
same fact twice -- so the mark goes and the command is drawn the way every
other verbatim thing in this app is: highlighted, monospace, on the raw
surface. The glyph stays for the kinds whose description is prose, and for a
command a provider never named.

Tapping one landed the tool card against the bottom edge of the screen, since
a reversed list anchors an item by its bottom -- so a tall card arrived at its
last line. A card that fits the viewport is centred now, and one that does not
has its top put at the top, which is where reading it starts. Only for a
journey the reader asked for: a restore still puts them back exactly where
they stopped.

The panel's own close chevron is gone -- the drag, the scrim and Back all
close it -- and the count is drawn even when it is zero, so "nothing is
running" and "nobody has asked yet" stop looking identical. There is then
nothing to expand, so that heading carries no chevron either.

Checked on the emulator against the sandbox: the card centred in a
mid-transcript tap, sat at the newest end where the list clamps, and the
zero heading drew with no control.

app/androidApp/src/main/kotlin/com/example/aiapp/AppRoot.kt

@@ -282,7 +282,6 @@ fun AppRoot(
                                     summary = here.summary,
                                     active = active,
                                     backgroundTasks = backgroundTasks,
-                                    onClose = close,
                                     onOpenSubagent = { screen = here.copy(subagent = it) },
                                     // Closed with it: what the reader asked to see is under this
                                     // panel, and a panel left open over the answer is the one