Coarse-graining support: Support.Sobolev.W1p.ConvexApproxSmoothing

Imported from the Apache-2.0 CoarseGraining development at commit c7ddd76c08ade64fed1b8d2ca51be14dfee8deb4.

Convex-domain smoothing operator (aggregate re-export)

Previously a 3373-line monolithic module; now split along thematic boundaries into the seven files imported above. This shim re-exports everything so existing downstream consumers keep working unchanged.