[codex] Add overlapping via pad short reproduction

[seveibar]

Reproduction

• adds a minimal reproduction using the exact GPIO35/BOOT and PSRAM via coordinates from spi-display-webcam-interceptor
• verifies the two 0.6 mm via copper pads overlap by about 0.033 mm while their 0.3 mm drill holes remain about 0.267 mm apart
• records that both checkDifferentNetViaSpacing and the complete runAllRoutingChecks pipeline currently return no diagnostic
• adds a PCB SVG snapshot that visibly shows the copper-pad intersection with no DRC overlay

This PR intentionally records current behavior only. A follow-up fix can change the expectation when different-net via copper-pad overlap is checked independently of drill-hole spacing.

Root cause captured

checkDifferentNetViaSpacing currently calculates clearance from hole_diameter. That enforces the manufacturing drill-hole spacing rule, but it does not detect overlapping outer_diameter copper pads on different nets.

Related autorouter reproduction: tscircuit/tscircuit-autorouter#2147

Verification

• bun test (175 pass, 6 snapshots)
• bun run build
• bunx tsc --noEmit
• bunx biome format tests/repros/repro-overlapping-different-net-via-pads.test.ts
• visual snapshot rendered and inspected