feat: add export_drill tool (kicad-cli, full drill option set)

New MCP tool `export_drill` wrapping `kicad-cli pcb export drill`:
format (excellon/gerber), drill origin, Excellon zero-suppression and
oval formats, units, mirror-Y, minimal header, separate PTH/NPTH files,
drill map generation + map format, and Gerber precision. Self-contained
interface handler reading the saved .kicad_pcb.

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

src/tools/registry.ts

@@ -59,6 +59,7 @@ export const toolCategories: ToolCategory[] = [
     tools: [
       "export_gerber",
       "export_gerbers",
+      "export_drill",
       "export_pdf",
       "export_svg",
       "export_3d",