Add a collapsible tree view of the SVG DOM in a sidebar tab.
- Click a tree node to highlight the element in the preview and scroll to it in the editor
- Bidirectional sync: preview ↔ tree ↔ editor
- Show element type, id, and key attributes
- Ref: vscode-svg2 DocumentSymbol tree in outline panel
Add a collapsible tree view of the SVG DOM in a sidebar tab.