feat: enhance workspace dock, reorganize menus, fix Reclass Dark theme

- Workspace dock: show member count per type, expandable child rows
  (Type Name format, Hex padding filtered), search/filter box with
  recursive matching, collapsed by default, double-click navigates
  to member in editor
- Menu reorganization: Import/Export submenus, new Tools menu (Type
  Aliases, MCP Server, Options), Data Source moved to View, renamed
  Unload→Close Project, Unsplit→Remove Split, Current Tab Source→
  Data Source
- View menu: add Relative Offsets toggle (persisted, applies to all
  editors and new splits)
- Fix Reclass Dark theme: hover/selected colors were identical to
  background (#1e1e1e), now #2a2a2a/#2a2d2e for visible contrast
- Dim MDI tab text via QPalette::WindowText (Fusion ignores CSS color)
- Remove dead QProxyStyle tab handlers (never called for QMdiArea)

src/mainwindow.h

@@ -11,6 +11,8 @@
 #include <QDockWidget>
 #include <QTreeView>
 #include <QStandardItemModel>
+#include <QSortFilterProxyModel>
+#include <QLineEdit>
 #include <QMap>
 #include <QButtonGroup>
 #include <QPushButton>
@@ -137,11 +139,13 @@ private:
     RcxEditor* activePaneEditor();
 
     // Workspace dock
-    QDockWidget*        m_workspaceDock  = nullptr;
-    QTreeView*          m_workspaceTree  = nullptr;
-    QStandardItemModel* m_workspaceModel = nullptr;
-    QLabel*             m_dockTitleLabel = nullptr;
-    QToolButton*        m_dockCloseBtn   = nullptr;
+    QDockWidget*          m_workspaceDock   = nullptr;
+    QTreeView*            m_workspaceTree   = nullptr;
+    QStandardItemModel*   m_workspaceModel  = nullptr;
+    QSortFilterProxyModel* m_workspaceProxy = nullptr;
+    QLineEdit*            m_workspaceSearch = nullptr;
+    QLabel*               m_dockTitleLabel  = nullptr;
+    QToolButton*          m_dockCloseBtn    = nullptr;
     void createWorkspaceDock();
     void rebuildWorkspaceModel();
     void updateBorderColor(const QColor& color);