Remove Gaussian/SciPy (PR #11), restore strict MATLAB-faithful H-kernel implementation

[Copilot]

PR #11 replaced the intended MATLAB construction with an isotropic Gaussian boundary integral using scipy.special.ndtr, which has no equivalent in any MATLAB source file and incorrectly rendered n as a no-op. This PR reverts that substitution and implements the correct MATLAB-derived evaluator.

Core mathematical change

The public evaluator imp_spline_2d now uses the H-kernel boundary integral — derived from MATLAB H.m via Green's theorem:

f(x,y) = ∮_{∂Ω CCW} (1 − H(Δx + δ/2, δ, n)) · H′(Δy + δ/2, δ, n) dy

• Additive: internal decomposition edges cancel to floating-point precision — no seams, no normalization hacks
• delta and n match MATLAB H.m semantics exactly; field is C^(n−1)
• No SciPy dependency; no Gaussian anywhere in the public API

MATLAB-to-Python primitive mapping

MATLAB	Python
H.m	H(t, delta, n)
Lxy.m / Lxy00.m	lxy(...) / lxy00(...)
Point_imp.m	point_imp(...)
LineSeg_imp.m	line_seg_imp(...)
L_corner_inter.m	l_corner_inter(...)
U_Angle_inter.m	u_angle_inter(...)
Square_Angle_inter.m	square_angle_inter(...)
ImpSpline2D.m	convex_product_spline_2d(...)

Key fixes

• core.py: Removed scipy.special.ndtr; replaced with H-kernel boundary integral. All MATLAB primitives ported with source-file citations. Default quadrature order raised 16 → 96 (the narrow compact support of H′ requires sufficient GL nodes to avoid ~66% integration error on large polygons).
• requirements.txt: Removed scipy>=1.7.
• __init__.py: Exports all new MATLAB primitives; version → 0.2.0.
• tests/: Removed 3 Gaussian-specific tests (rotation invariance, C^∞ contour sharpness, grid refinement). Added MATLAB parity tests for every primitive and C^(n−1) smoothness validation consistent with MATLAB's claimed behaviour.

[Copilot]

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