feat(M14.6): add continuum kernel/operator double copy

[jagg-ix]

Scope

Adds the missing continuous base-space and two-point-kernel layer above the existing M14 finite/infinite graph sequence.

• places Jacobi-compatible numerator triples on X × X;
• integrates the weighted double-copy density through a convergent continuum quadrature;
• verifies finite Hilbert--Schmidt norm behavior;
• checks pointwise and integral generalized-gauge invariance;
• exercises commuting left/right continuum multipliers;
• evaluates zero and positive pointwise-background kernel composition;
• adds standalone registration, test, formal ledger, ZIL graph, and documentation.

Formal authority

Pinned to jagg-ix/entropic-physlib-private, branch entropic-physlib-linear-full, tip 35f98f147771a4e250ec01b4cbf2afab72313db7, including the current BCJ, scalar-continuum, pointwise-operator, and Lp/a.e.-convergence blobs.

Toolchain

• Lean 4.31.0 / leanprover/lean4:v4.31.0
• jagg-ix/zil-lean@6daee2698304feb203c6adb91b2e8853613f85b5

Validation

pytest -q tests/test_m14_continuum_kernel_double_copy_m146.py
1 passed

The study closes all 8 acceptance groups.

Claim boundary

This is an explicit L2/Hilbert--Schmidt quadrature carrier. Measurability, maximal-domain, summability, and weighted-orthogonality premises remain visible; no arbitrary interacting continuum double-copy theorem is inferred.

Merge audit

• targets main directly;
• based on 93607ae7c147e071fe62d6f4c0a2d182f276477d;
• six new files only;
• no CI/workflow changes;
• no file overlap with M14.5 or M14.7.

Recommended merge order is M14.5, then M14.6, although this branch has no code import dependency on M14.5.