Full keyboard mode, Ctrl/Alt/Super, dead keys, shift levels

- Full (iPad Pro) mode: every typing key from the keymap, number row,
  tab, caps lock, ctrl/super/alt; shifted symbol shown above and flickable
- Dead keys compose with the locale's XKB compose table
- Ctrl/Alt/Super stick like shift and turn keys into shortcuts; a tapped
  or held shift joins shortcuts and non-text keys, auto-shift and caps
  lock don't
- Auto-capitalization and caps lock only capitalize letters; the user's
  shift picks the keymap's shifted level
- Mode switch in settings keeps key size by resizing the window

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/settings/Settings.cpp

@@ -8,6 +8,7 @@ namespace {
 constexpr auto AutoCapitalizeKey = "typing/autoCapitalize";
 constexpr auto DoubleSpacePeriodKey = "typing/doubleSpacePeriod";
 constexpr auto VisibleSectionsKey = "layout/visibleSections";
+constexpr auto FullKeyboardKey = "layout/fullKeyboard";
 }
 
 Settings::Settings(QObject *parent)
@@ -20,6 +21,16 @@ Settings::Settings(QObject *parent)
     m_visibleSections = store.value(VisibleSectionsKey, QStringList{MainSectionId}).toStringList();
     if (m_visibleSections.isEmpty())
         m_visibleSections = {MainSectionId};
+    m_fullKeyboard = store.value(FullKeyboardKey, false).toBool();
+}
+
+void Settings::setFullKeyboard(bool full)
+{
+    if (full == m_fullKeyboard)
+        return;
+    m_fullKeyboard = full;
+    QSettings().setValue(FullKeyboardKey, full);
+    Q_EMIT fullKeyboardChanged();
 }
 
 void Settings::setSectionVisible(const QString &id, bool visible)