fix(core): prevent unbounded slab corner miters

[wass08]

Summary

• bound slab corner miters so near-parallel wall-offset edges cannot create runaway vertices
• fall back to local offset endpoints for non-finite or over-limit intersections
• add the exact copied Wawa House slab and wall coordinates as a regression test

Root cause

Two consecutive stored slab edges were nearly collinear but received slightly different wall-derived offsets. Intersecting their infinite offset lines amplified the tiny angular difference into a vertex 44,952 m away.

Test plan

• bun run build
• bun run check-types
• bun test in packages/core (942 passing)
• recomputed all 15 slabs in the copied Wawa House draft with no unbounded coordinates

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Note

Low Risk
Localized change to render-time corner joining in slab-polygon with a conservative ratio cap and existing parallel-edge fallback; regression test covers the reported case.

Overview
Renderable slab polygons no longer blow up when two consecutive edges are almost collinear but get slightly different wall offsets. Corner construction still intersects offset lines for normal miters, but if the intersection is non-finite or the miter reaches farther than 10× the larger edge offset (MAX_CORNER_MITER_RATIO), it falls back to the two local offset endpoints instead of a runaway vertex (the failure mode that produced ~45 km spikes).

A regression test uses real Wawa House slab/wall coordinates and asserts the rendered ring stays near the stored footprint (extent and longest edge bounds).

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