refactor(model): collapse the thread list to a single column

Five columns answered through Qt::DisplayRole; one column cannot, and a card
needs every field at once, so each gets its own role. Qt::DisplayRole keeps
answering the subject, which is what keyboard search and accessibility read.

Three things change shape rather than moving. DateRole hands over the QDateTime
itself, since the card decides how much of a date it has room for and a
pre-formatted string takes that decision away from the delegate. The subject
loses its "(3)" message-count suffix, which the reply count on line 2 now
states. And the two per-column tooltips become one card-wide tooltip, because
the marks no longer have columns of their own to hover.

The build is red at this commit: the view and the delegates still name the
deleted Column enumerators and are rewritten in the commits that follow.

1 files changed, 20 insertions, 29 deletions

diff --git a/src/threadlistmodel.h b/src/threadlistmodel.h
index b13165c..9cb774e 100644
--- a/src/threadlistmodel.h
+++ b/src/threadlistmodel.h
@@ -38,26 +38,6 @@ class ThreadListModel : public QAbstractItemModel
 {
     Q_OBJECT
 public:
-    /// No tags column: spelling out a dozen tags per row cost most of the
-    /// list's width and was unreadable. Functional tags moved to a chip strip
-    /// under the message pane, and the account tag renders as a chip in front
-    /// of the subject.
-    enum Column {
-        /// A paperclip when the thread has an attachment, so it is visible
-        /// without opening the thread. Icon only and deliberately narrow;
-        /// it carries no text.
-        AttachmentColumn = 0,
-
-        /// A star when the thread carries the flagged tag. Beside the
-        /// paperclip and the same shape: icon only, narrow, no text.
-        FlagColumn,
-
-        DateColumn,
-        AuthorsColumn,
-        SubjectColumn,
-        ColumnCount,
-    };
-
     enum Role {
         /// The thread id behind a row. Views hand out QModelIndexes, but the
         /// worker speaks thread ids, so the mapping belongs on the model
@@ -123,20 +103,33 @@ public:
         /// TagColors instance, and a delegate reading config itself would be a
         /// second source of truth.
         MessageOwnColoursRole,
+
+        /// The card's own fields, by role rather than by column.
+        ///
+        /// Five columns used to answer these through Qt::DisplayRole. One
+        /// column cannot, and a card needs all five values at once, so each
+        /// gets a role and Qt::DisplayRole answers the subject alone (which is
+        /// what keyboard search and accessibility read).
+        SubjectRole,
+        SendersRole,
+        DateRole,          ///< A QDateTime. The delegate formats it.
+        HasAttachmentRole, ///< bool
+        IsFlaggedRole,     ///< bool
+        ReplyCountRole,    ///< int; 0 when a thread has no replies.
     };
 
-    /// Row fill for a thread tagged `deleted`, and for one tagged `spam`.
-    /// Muted rather than saturated: a bulk delete paints every selected row,
-    /// and a wall of pure red is harder to read than the list it replaces.
-    /// Exposed so a test names the same colour the model uses.
-    /// The character shown in AttachmentColumn for a thread that has one.
-    /// A paperclip when the system font can draw it, "*" otherwise.
+    /// The mark drawn on a card's second line when the message has an
+    /// attachment. A paperclip when the system font can draw it, "*" otherwise.
     static QString attachmentGlyph();
 
-    /// The character shown in FlagColumn for a flagged thread.
+    /// The mark drawn on a card's second line when the message is flagged.
     /// A star when the system font can draw it, "*" otherwise.
     static QString flagGlyph();
 
+    /// Row fill for a thread tagged `deleted`, and for one tagged `spam`.
+    /// Muted rather than saturated: a bulk delete paints every selected row,
+    /// and a wall of pure red is harder to read than the list it replaces.
+    /// Exposed so a test names the same colour the model uses.
     static QColor deletedColour();
     static QColor spamColour();
 
@@ -183,8 +176,6 @@ public:
     /// nothing.
     bool hasChildren(const QModelIndex &parent = {}) const override;
     QVariant data(const QModelIndex &index, int role) const override;
-    QVariant headerData(int section, Qt::Orientation orientation,
-                        int role) const override;
 
     void appendBatch(const QVector<ThreadSummary> &batch);
     void clear();