Full keyboard: stagger the letter rows like a hardware keyboard

- The ISO key left of Z takes its room from left shift (2.25 → 1.25 + 1),
  so ISO layouts no longer make the shift row the widest
- Caps lock and left shift keep their width; only right-hand keys stretch,
  so A no longer lines up with the key below it

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

tests/tst_layoutbuilder.cpp

@@ -110,6 +110,20 @@ private Q_SLOTS:
         QCOMPARE(letterKey(us, u"1"_s).shifted, u"!");
     }
 
+    void fullModeRowsStagger()
+    {
+        // The key ahead of A, and of the first key on the Z row: like a hardware keyboard,
+        // with the ISO key (sk: |) taking its room from left shift.
+        const auto offsets = [](const Layout &layout) {
+            const QList<Row> &rows = layout.layers.first().rows;
+            return std::pair{rows[2].first().width, rows[3].first().width};
+        };
+        QCOMPARE(offsets(TestLayouts::build("us", KeyboardMode::Full)), std::pair(1.75, 2.25));
+        const Layout sk = TestLayouts::build("sk", KeyboardMode::Full);
+        QCOMPARE(offsets(sk), std::pair(1.75, 1.25));
+        QCOMPARE(sk.layers.first().rows[3].at(1).label, u"\\"_s);
+    }
+
     void fullModeKeepsDeadKeysAndKeymapShift()
     {
         const Layout sk = TestLayouts::build("sk", KeyboardMode::Full);