circuits/audio_chain.py wires stages 1/1b/2/3/4 with shared nets and deduplicated
parts: ONE OPA1612 (U4) does both the Stage-2 filter (A) and Stage-3 summer (B);
ONE ULN2003 (U6) drives all three relays (K1 select, K2 mute, K3 ground-lift).
54 components, ERC 0 errors, netlist 0 errors. Per-stage files remain as the
documented, individually-simulated building blocks.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
