Add class keyword picker, alignas alignment picker with member realignment

- Class keyword (struct/class/union/enum) persists in JSON, drives generator output
- CommandRow2 shows alignas(N) pill computed from struct member alignment
- Clicking alignas opens picker (1, 4, 8, 16) to realign all members
- Going up: members repositioned to N-byte boundaries, padding fills gaps
- Going down: excess padding removed, members pack tighter
- Add cmd::ChangeOffset for undoable offset repositioning
- All 11 tests pass

Co-Authored-By: combuter <combuter@users.noreply.github.com>

src/editor.h

@@ -44,6 +44,7 @@ public:
 
     void applySelectionOverlay(const QSet<uint64_t>& selIds);
     void setCommandRowText(const QString& line);
+    void setCommandRow2Text(const QString& line);
     void setEditorFont(const QString& fontName);
     static void setGlobalFontName(const QString& fontName);
 
@@ -76,7 +77,6 @@ private:
     // ── Hover cursor + highlight ──
     QPoint m_lastHoverPos;
     bool   m_hoverInside = false;
-    bool   m_cursorOverridden = false;
     uint64_t m_hoveredNodeId = 0;
     int      m_hoveredLine = -1;
     QSet<uint64_t> m_currentSelIds;