dbar-solvability: the dbar-equation on Riemann surfaces (namespace RS)

API summary (see docs/design/dbar-solvability.md). Zero sorries throughout.

• Planar core (mathlib-only): wirtingerD/wirtingerDbar + the CR bridge (Wirtinger.lean); cauchyKernel/cauchyTransform and Forster 13.1 (exists_dbar_solution_of_hasCompactSupport, CauchyKernel.lean); Forster 13.2 on disks (exists_dbar_solution_ball, SolveDisk.lean); finite smooth partitions of unity (exists_smooth_partition_of_finite_cover, PlanarPoU.lean); the planar Cousin atoms (exists_smooth_splitting/exists_holo_splitting_ball, PlanarCousin.lean).
• Surface layer: Form01 X (chart-coefficient (0,1)-forms, Form01.lean); SmoothC X, the intrinsic dbar : SmoothC X →ₗ[ℂ] Form01 X, IsDbarAt/IsDbarOn, contMDiffOn_omega_of_isDbarOn_zero, contMDiffOn_omega_sub_of_isDbarOn, and chart-disk solvability exists_dbar_solution_chart_ball (Operator.lean).
• Disk acyclicity (DiskAcyclic.lean): subsingleton_h1Cover_zero_of_isChartDisk, the D = 0 case of Čech H¹ vanishing on chart-disk covers — the general-divisor twist is NOT included (see the file's docstring and the build log for the honest scope note).