feat(config): add the trash query generator

Adds trash as a fifth built-in query filter beside Unread, Inbox,
Important and Sent, composing per-account exactly as Sent does:
Config::resolvedQuery() asks each account for its own trashQuery()
rather than wrapping the all-accounts union, and an account with no
trash folder resolves to matchNothingQuery() rather than "match
everything".

Also gives the Trash button a toolbar icon (user-trash) and a trash
key to the mainwindow fixture that asserts every filter button carries
one; without it the button is skipped from the row entirely (no
account configured a trash folder), and the existing icon test found
no button to check.

1 files changed, 13 insertions, 3 deletions

diff --git a/tests/test_mainwindow.cpp b/tests/test_mainwindow.cpp
index b188ef4..7316689 100644
--- a/tests/test_mainwindow.cpp
+++ b/tests/test_mainwindow.cpp
@@ -7922,10 +7922,20 @@ void TestMainWindow::everyBuiltinFilterButtonCarriesAnIconAndItsText()
     // which is the same argument the Save button records.
     QTemporaryDir dir;
     QVERIFY(dir.isValid());
-    Config config;
-    config.load(writeSentConfig(dir, {
+    const QString path = writeSentConfig(dir, {
         {QStringLiteral("work"), QStringLiteral("Sent")},
-    }));
+    });
+    // A trash key too, or the Trash filter finds nothing and is skipped from
+    // the row entirely (item 103), leaving no trashButton for this loop to
+    // find.
+    {
+        QSettings s(path, QSettings::IniFormat);
+        s.beginGroup(QStringLiteral("account.work"));
+        s.setValue(QStringLiteral("trash"), QStringLiteral("Trash"));
+        s.endGroup();
+    }
+    Config config;
+    config.load(path);
 
     MainWindow window(config);