feat: add export_pcb_svg tool (kicad-cli, full layer-plot SVG)

New MCP tool `export_pcb_svg` wrapping `kicad-cli pcb export svg`: exposes
the full layer-plot surface (layer/common-layer lists, mirror, soldermask
subtraction, negative, B&W, theme, the four DNP fab-layer modes,
page-size-mode, fit-page-to-board, exclude-drawing-sheet, drill-shape, and
the single/multi output modes). Rich CLI sibling of the existing SWIG
export_svg (left untouched). Reads the saved .kicad_pcb.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/tools/registry.ts

@@ -66,6 +66,7 @@ export const toolCategories: ToolCategory[] = [
       "export_gencad",
       "export_pos",
       "export_pcb_pdf",
+      "export_pcb_svg",
       "export_pdf",
       "export_svg",
       "export_3d",