feat: add export_sch_hpgl tool (kicad-cli, schematic HPGL)

New MCP tool `export_sch_hpgl` wrapping `kicad-cli sch export hpgl`: outputs
one plot per page into a directory. Exposes drawing-sheet override,
exclude-drawing-sheet, default-font, page selection, pen size, and the
origin/scale mode. schematicPath required; directory output uses outputDir.

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

src/tools/registry.ts

@@ -74,6 +74,7 @@ export const toolCategories: ToolCategory[] = [
       "export_sch_pdf",
       "export_sch_svg",
       "export_sch_dxf",
+      "export_sch_hpgl",
       "export_pdf",
       "export_svg",
       "export_3d",