fix: use the copper outline of hole_with_polygon_pad plated holes in clearance checks

[mvennarini]

Fixes #260

Summary

getPolygonPointsForPad, getPolygonShape, getPadBounds and getCollidableBounds only recognised rect-pad plated holes, so a hole_with_polygon_pad plated hole was reduced to its drill (or to a zero-size box for oval/pill drills, where hole_diameter is undefined). A different-net via, SMT pad or trace on the polygon copper away from the drill passed checkViasInPads, checkPadPadClearance, checkViaPadClearance and checkPadTraceClearance with no errors.

• add getPolygonPadHolePoints / isPolygonPadHole: pad_outline is relative to the hole position and rotated by ccw_rotation, the same convention checkCopperToBoardEdgeClearance and core's PlatedHole already use
• getPolygonPointsForPad returns those points, so every clearance check that goes through getPadToPadGap / getTraceObstacleClearance sees the real copper
• getPadBounds and getCollidableBounds derive the spatial-index bounds from the outline instead of getBoundsOfPcbElements (which only knows the drill for this shape; a matching fix for the util is in tscircuit/circuit-json-util, but this PR does not depend on it)

Rect-pad, pill, circle and SMT pad paths are unchanged.

Tests

tests/lib/check-polygon-pad-plated-hole.test.ts covers, for a 4mm x 4mm polygon pad with a 0.8mm drill:

• via fully inside the copper, 1.5mm from the drill: checkViasInPads reports it
• via 0.05mm outside the outline: checkViaPadClearance reports it
• SMT pad on the copper: checkPadPadClearance reports it
• 0.2mm trace 0.05mm from the outline: checkPadTraceClearance reports actual_clearance 0.05mm
• 6mm x 1mm bar with ccw_rotation: 90: a via at (0, 2.5) is reported, a via at (2.5, 0) is not

All five fail on main (0 errors) and pass with this change.

Verification

• bun test (246 pass)
• bunx tsc --noEmit
• bunx biome format lib tests

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https://claude.ai/code/session_012Tbs6mJUsouNVBTYJndPuf