fix: close project actually destroys dock, editor perf single-pass line attributes

- Set WA_DeleteOnClose on doc docks so all close paths trigger cleanup
- Create fresh empty class when last project closes
- Add splitDockWidget/resizeDocks to project_new() so workspace doesn't eat editor space
- Merge applyMarginText, applyMarkers, applyFoldLevels into single-pass applyLineAttributes
- Cache line texts for heatmap/symbol coloring passes (avoid redundant Scintilla IPC)
- Zero-alloc scroll width scan replaces QString::split

src/main.cpp

@@ -3227,6 +3227,13 @@ QDockWidget* MainWindow::project_new(const QString& classKeyword) {
                                        currentCtrl->activeSourceIndex());
     }
 
+    // Ensure workspace dock is split alongside editor with sensible proportions
+    if (m_docDocks.size() == 1 && m_workspaceDock) {
+        splitDockWidget(m_workspaceDock, m_docDocks.first(), Qt::Horizontal);
+        resizeDocks({m_workspaceDock}, {128}, Qt::Horizontal);
+        m_workspaceDock->show();
+    }
+
     rebuildWorkspaceModel();
     return dock;
 }