Reorganize Riemannian/Util/ into themed sub-directories

[Xinze-Li-Moqian]

Current state

OpenGALib/Riemannian/Util/ has 15 files (2839 LOC) flat, no sub-grouping. Per Riemannian/Util/README.md, the files cluster into 5 themes:

Theme	Files	LOC
Chart Jacobian	ChartJacobianSmooth, ChartJacobianSmoothness, FlatChartDerivs	915
Tangent / section glue	TangentHelpers, TangentSpaceInstances, TensorBundleCoercions, MfderivApplySection	872
Metric inner / Riesz / notation	MetricInnerSmoothness, MetricNotation, MetricRieszBilinForm, CotangentFunctional	569
Covariant derivative	CovDerivBridges, CovDerivSmoothness	401
Operator simp lemmas	ConnectionLaplacianSimp, DivergenceSimp	82

Proposed restructure

Sub-directories matching the 5 themes:

• Util/Chart/ — ChartJacobianSmooth, ChartJacobianSmoothness, FlatChartDerivs
• Util/Tangent/ — TangentHelpers, TangentSpaceInstances, TensorBundleCoercions, MfderivApplySection
• Util/Metric/ — MetricInnerSmoothness, MetricNotation, MetricRieszBilinForm, CotangentFunctional
• Util/CovDeriv/ — CovDerivBridges, CovDerivSmoothness
• Util/Simp/ — ConnectionLaplacianSimp, DivergenceSimp

Each sub-dir gets its own one-paragraph README. Main Riemannian/Util/README.md adjusts to reference sub-dirs.

Cascade

Every import OpenGALib.Riemannian.Util.X must update to import OpenGALib.Riemannian.Util.<Theme>.X. ~20-30 consumer files.

Acceptance

• Build clean
• lake exe shake baseline maintained
• Sorry count unchanged
• All linters pass at current baselines