Parses external netlist files into the component-pin-net graph that
verify_connectivity and apply_batch consume. Supports KiCad XML (.net)
exported by kicad-cli, and CSV/TSV with flexible column name matching.
Auto-detects format from file extension and content. Output is directly
compatible with verify_connectivity's expected parameter, closing the
loop between "I have a design" and "I can build it in KiCad."
Requested by ESP32-P4 project (agent thread message 028).
