feat: add plated hole drill-to-drill clearance DRC check

[zkasuran]

What

Adds checkPlatedHoleDrillClearance, a DRC check that flags pairs of plated holes whose drilled holes sit closer than the minimum drill edge to drill edge clearance. This implements the "Pad Hole-to-Hole Spacing" item tracked in #15.

Why

min_plated_hole_drill_edge_to_drill_edge_clearance (0.15mm on JLCPCB) is defined in @tscircuit/jlcpcb-manufacturing-specs and can be set per board, but no check reads it today. Two plated holes drilled too close cannot be fabricated reliably: the web of material between the holes breaks down and the drill can wander or break out. The current checks miss this:

• checkPadPadClearance measures the copper pad edges rather than the drill. It also skips same-net pairs, so two same-net through holes can sit with their drills almost touching and still pass.
• checkSameNetViaSpacing and checkDifferentNetViaSpacing only look at pcb_via, not pcb_plated_hole.

So a board that should error returns []. Minimal repro: two same-net plated holes with 0.05mm annular rings (so the copper does not overlap) whose drills sit 0.12mm apart.

// hole_diameter 0.5, outer_diameter 0.6, centers 0.62mm apart, same net
{ "type": "pcb_plated_hole", "shape": "circle", "pcb_plated_hole_id": "PH1", "x": 0,    "y": 0, "hole_diameter": 0.5, "outer_diameter": 0.6, ... }
{ "type": "pcb_plated_hole", "shape": "circle", "pcb_plated_hole_id": "PH2", "x": 0.62, "y": 0, "hole_diameter": 0.5, "outer_diameter": 0.6, ... }

runAllChecks returns [] on this board before this change and a single pcb_pad_pad_clearance_error after it.

How

• Each plated hole's drill (not its copper pad) is modeled as a capsule, a line segment plus a radius. A round hole is a degenerate capsule, an oval or pill hole is a segment as long as the elongation capped by a radius of half the short axis. The gap is segmentToSegmentMinDistance minus the two radii, so circle, oval, pill and the rect-pad hole variants are all handled, including hole_offset and rotation.
• The check is net independent, because drill spacing is a constraint on the drill step rather than an electrical one. This mirrors checkSameNetViaSpacing, which enforces via hole spacing regardless of connectivity. Copper pad clearance stays in checkPadPadClearance.
• Two holes at the same location are skipped as a placement duplicate, the same way the via spacing checks do.
• Wired into runAllPlacementChecks next to checkPadPadClearance and exported from the index.

Tests

• Too close returns one error, sufficiently spaced returns none, coincident duplicates return none, oval drills too close are flagged.
• A same-net board where checkPadPadClearance returns [] while this check returns one error.
• runAllChecks on that same board returns exactly the new error, which nothing caught before.
• An error-drawn SVG snapshot of the two holes.

Verified locally, all green: bun test (148 pass), bunx tsc --noEmit, bun run format:check, bun run build, bunx @tscircuit/dependency-check.

AI assistance

I used AI assistance (Claude) while writing this change. I designed the approach, reviewed the code and verified the behavior myself. Verified locally before submitting: bun test (148 pass, including the new file), bunx tsc --noEmit, bun run format:check, bun run build and bunx @tscircuit/dependency-check all pass.