Optional PC key blocks: function row, navigation, numeric keypad

- Template sections placed above or to the right of the typing keys;
  the user picks any mix in settings, typing keys included
- keysym keys send XKB keysyms on press, optionally repeating
- Geometry lays blocks side by side with one key unit; stretch keys are
  resolved at layout time so composed blocks line up
- Toggling a block resizes the window so keys keep their size

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

src/layout/Layout.h

@@ -16,6 +16,7 @@ enum class KeyType {
     Dismiss,
     Spacer, // empty room, e.g. the half-key indent of the home row
     Letters, // template only: a row of letters from the system keymap
+    Keysym,  // a non-text key (Home, F5, arrows...): sends `keysym`
 };
 
 struct KeyDef {
@@ -26,7 +27,9 @@ struct KeyDef {
     QStringList alternates; // long-press choices
     QString target;         // layer to switch to (LayerSwitch only)
     qreal width = 1.0;      // in key units
-    bool stretch = false;   // grows so the row is as wide as the layer's widest
+    bool stretch = false;   // grows so the row is as wide as its block's widest
+    quint32 keysym = 0;     // Keysym keys only
+    bool repeat = false;    // Keysym keys only: auto-repeat while held
 
     // Letters placeholders only.
     int lettersRow = -1;    // which keymap row (0 = top)
@@ -48,10 +51,21 @@ struct Layer {
     QList<Row> rows;
 };
 
+// An optional block of keys next to the main one, shown if the user wants it.
+struct Section {
+    enum class Placement { Above, Right }; // above the main keys, or a column to their right
+
+    QString id;   // "main" is reserved for the layers
+    QString name; // shown in settings
+    Placement placement = Placement::Right;
+    QList<Row> rows;
+};
+
 struct Layout {
     QString id;
     QString name;        // human readable, e.g. "Slovak"
-    QList<Layer> layers; // the first one is shown by default
+    QList<Layer> layers; // the main keys; the first one is shown by default
+    QList<Section> sections;
     // Template only: long-press choices for keymap letters, by lowercase letter.
     QHash<QString, QStringList> alternates;
 
@@ -64,3 +78,5 @@ struct Layout {
         return nullptr;
     }
 };
+
+inline const QString MainSectionId = QStringLiteral("main");