Theme system overhaul, UI polish, and VS2022 Dark theme

- Replaced hardcoded theme factories with JSON files + CMake build step
- Shared ThemeFieldMeta table for DRY serialization and editor UI
- Fixed live preview (auto-triggers on color change, no toggle button)
- Fixed duplicate theme entries when editing built-in themes
- Moved title bar from icon to bold "Reclass" text with View > Show Icon toggle
- MDI tabs: 24px height, unicode close button styled like TypeSelectorPopup
- Added VS2022 Dark theme with purple accent colors
- Status bar padding, removed monospace font overrides on tabs/statusbar
- Default startup opens Ball demo + Unnamed hex64 tabs

src/themes/themeeditor.h

@@ -36,14 +36,10 @@ private:
     QComboBox*   m_themeCombo   = nullptr;
     QLineEdit*   m_nameEdit     = nullptr;
     QLabel*      m_fileInfoLabel = nullptr;
-    QPushButton* m_previewBtn   = nullptr;
-    bool         m_previewing   = false;
 
     void loadTheme(int index);
-    void rebuildSwatches(QVBoxLayout* swatchLayout);
     void updateSwatch(int idx);
     void pickColor(int idx);
-    void togglePreview();
 };
 
 } // namespace rcx