Use one frame for schematic roundtrip snapshots

[ShiboSoftwareDev]

Summary

• render each open-source schematic reference and its round-trip output in the same reference-paper coordinate frame
• preserve the existing explicit enlarged frame for the HERON PAY-SSM off-sheet fixture
• refresh NodeMCU, SimpleFOC Mini, SimpleFOC Shield, and HERON systems snapshots so placement and paper-size differences are visible at one scale

Validation

• bun run typecheck
• bun test tests/schematic-roundtrip01-nodemcu-esp12.test.ts
• bun test tests/schematic-roundtrip02-heron-pay-ssm.test.ts
• bun test tests/schematic-roundtrip03-simplefoc-mini.test.ts
• bun test tests/schematic-roundtrip04-simplefoc-shield-v3.test.ts
• bun test tests/schematic-roundtrip05-heron-systems-pcb.test.ts

Stacked on #69 because the shared schematic view-box API is pinned there.