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/mainwindow.h

@@ -107,6 +107,7 @@ private:
     SplitPane createSplitPane(TabState& tab);
     void applyTheme(const Theme& theme);
     void applyTabWidgetStyle(QTabWidget* tw);
+    void styleTabCloseButtons();
     SplitPane* findPaneByTabWidget(QTabWidget* tw);
     SplitPane* findActiveSplitPane();
     RcxEditor* activePaneEditor();