feat: add export_sch_pdf tool (kicad-cli, schematic PDF)

New MCP tool `export_sch_pdf` wrapping `kicad-cli sch export pdf`: exposes
the full option set (drawing-sheet override, theme, B&W,
exclude-drawing-sheet, default-font, the PDF property-popup /
hierarchical-link / metadata excludes, no-background-color, and page
selection). schematicPath is required and validated.

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

src/tools/registry.ts

@@ -71,6 +71,7 @@ export const toolCategories: ToolCategory[] = [
       "export_gerber_single",
       "export_3d_cli",
       "export_sch_bom",
+      "export_sch_pdf",
       "export_pdf",
       "export_svg",
       "export_3d",