feat: count a card's messages, not its repliesthread-row-identity

The expander pill read "N replies" while the row stood for the
conversation: a thread of one message and four replies said "4 replies"
over rows that listed all five messages. The user's model is messages, so
it now reads "5 messages". A thread of one still shows nothing: its row is
the message, the pill is the expander, and there is nothing to open.

ReplyCountRole becomes MessageCountRole and CardLayout::Input::replyCount
becomes messageCount, so the names stop lying about what they carry. The
label is now translated under a CardLayout context, with Italian
"messaggio"/"messaggi" shipped; %n's untranslated fallback on this Qt does
not pluralise, so the two forms are separate entries. The card's densest
geometry test needs 460px rather than 400 now that the pill is one
character wider.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/types.h b/src/types.h
index 8e24cd1..ee2627f 100644
--- a/src/types.h
+++ b/src/types.h
@@ -190,9 +190,9 @@ struct MessageNode
     QStringList tags;
     QString filePath;
 
-    /// Reply depth within the thread. 0 is the thread's first message, which
-    /// occupies the ROOT row rather than a child row: the user's model is
-    /// "N replies", so a thread of 7 shows 1 root and 6 descendants.
+    /// Reply depth within the thread. 0 is the thread's first message: since
+    /// item 177 a conversation lists it as a child row too, but it carries no
+    /// nesting. 1 is a direct reply.
     int depth = 0;
 
     bool isUnread() const { return tags.contains(QStringLiteral("unread")); }