SoftQP native engine

Contains modified OSQP and OSQP Python interface (Apache-2.0).
OSQP contributors: https://github.com/osqp/osqp
Generalized penalty implementation: A2R-Lab/osqp at 2500405a1bc63387721feec64f0c050fa99223dd.
Python binding: A2R-Lab/osqp-python at d6df7f987ba40e75bfac338ab19a97b2c92f7334.
OSQPSlack research repository: https://github.com/A2R-Lab/OSQPSlack (MIT).
Original notices and licenses are retained under native/.
The namespace and reproducible local-source build are modified for SoftQP.

SoftQP modifications include asymmetric projection, objective, conjugate, scaling
and recession paths, original-space contracts, compact/asymmetric lifting adapters
and the optional original-scale DAQP comparison. Modified files are marked.

SoftQP 0.2 adds original-row directional coupled peak kernels, original-space
group diagnostics and conservative recession certificates, exact compact/row-split
baselines, fixed-shape vector workspaces, explicit numeric-failure status and
IEEE NaN invalidation. Unsupported directional scaling, adaptive metrics, code
generation and sensitivities are rejected. These are research implementation
changes, with no claim of mathematical priority or computational superiority.
