RellichKondrachov.Geometry.Manifold.Sobolev.RellichKondrachovRiemannian

Thin re-export of the Riemannian Rellich–Kondrachov proof, split into focused submodules:

• RellichKondrachovRiemannian.Transport: L² transport (change of measure, extendByZero glue).
• RellichKondrachovRiemannian.Chartwise: chartwise compactness via Euclidean Rellich on volume.
• RellichKondrachovRiemannian.Global: finite-atlas assembly and the final compactness theorem.