import_svg fuses every path into one node - no way to select individual shapes after import

`import_svg` collapses every `` in the imported SVG into a single VECTOR node with no sub-groups - confirmed via `node_children` returning empty on the result. `export_svg` on the same node correctly returns every original shape/color, and the live canvas renders it correctly, so the geometry isn't lost - it's just unreachable afterward.

Repro: `import_svg` any multi-shape SVG (2+ `` elements), then call `node_children` on the resulting node - returns empty despite `export_svg` correctly showing all original shapes.

Why this matters: for agent-driven workflows specifically, there's no way to fix or adjust one element of an imported design afterward without discarding the whole import and rebuilding from source - the agent has no node to grab onto.

Feature request: preserve one node per top-level ``/`` on import (or an option to do so), so a multi-shape SVG import is editable the same way a hand-built multi-shape design is.

Environment: Windows 11, desktop app + `@open-pencil/mcp`/`@open-pencil/cli` both on the current release as of this report.