feat(ui): make the toolbar icon size configurable

Follow-up to item 56. With the toolbar now following the desktop's
button style, an "icon only" desktop makes the icon the whole control,
and this style reports PM_ToolBarIconSize as 16px, which is a small
target for a button with no text beside it.

A [general] toolbar_icon_size key, 16 to 64, defaulting to 24 rather
than to the style's own metric. Setting it to 16 restores the theme's
value.

Clamped and reported, unlike message_zoom, which documents a 0.5 to 3.0
range in the README and enforces none of it. Both ends here break the
UI that would be used to fix them: too small is an invisible icon, too
large is a toolbar taller than the window.

The unenforced message_zoom range is recorded as item 58 rather than
fixed here, since it is a separate defect that predates this change.

Also documents in the README that saved-query button labels are the key
names from the user's own [queries] section, which is why the "Flagged"
button still read that way after the action was renamed: it is a user's
query name, not a string this code owns. The sample config now shows
`Important = tag:flagged` to teach the wording the UI uses.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/tests/test_mainwindow.cpp b/tests/test_mainwindow.cpp
index 4a911c9..84a3a7d 100644
--- a/tests/test_mainwindow.cpp
+++ b/tests/test_mainwindow.cpp
@@ -120,6 +120,7 @@ private slots:
     void theToolbarDoesNotOverrideTheDesktopButtonStyle();
     void theImportantActionIsLabelledImportant();
     void theImportantActionStillWritesTheFlaggedTag();
+    void theToolbarUsesTheConfiguredIconSize();
 };
 
 void TestMainWindow::everyKnownActionIsRegistered()
@@ -2513,6 +2514,34 @@ void TestMainWindow::theImportantActionStillWritesTheFlaggedTag()
              "written, which no other tool reading this Maildir knows");
 }
 
+void TestMainWindow::theToolbarUsesTheConfiguredIconSize()
+{
+    // With the toolbar following the desktop's "Icon only" style, the icons are
+    // the whole control, and this style reports 16px, which is a small target.
+    // The size is configurable with a 24px default; this proves the config
+    // value actually reaches the widget rather than sitting in Config unread.
+    QTemporaryDir dir;
+    QVERIFY(dir.isValid());
+    const QString path = dir.filePath(QStringLiteral("qtmaildir.conf"));
+    QFile file(path);
+    QVERIFY(file.open(QIODevice::WriteOnly | QIODevice::Text));
+    file.write("[general]\ntoolbar_icon_size = 40\n");
+    file.close();
+
+    Config config;
+    config.load(path);
+    QCOMPARE(config.toolbarIconSize(), 40);
+
+    MainWindow window(config);
+    auto *toolBar = window.findChild<QToolBar *>(QStringLiteral("main_toolbar"));
+    QVERIFY(toolBar);
+
+    // 40 is deliberately not any of this style's own metrics (16 small, 32
+    // large), so the assertion cannot pass by the widget happening to agree
+    // with the theme.
+    QCOMPARE(toolBar->iconSize(), QSize(40, 40));
+}
+
 // Constructing a MainWindow needs a QApplication and a platform plugin. The
 // test has no display under ctest, so it runs offscreen unless the caller
 // asked for something else.