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>