Add sharpening support

[tfarago]

Summary

This makes the new frequency-sharpen UFO filter available from tofu as a user-facing sharpening option.

Changes

• Added a sharpening config section with --sharpen, --sharpen-method, --sharpen-strength, and --sharpen-lorentz-fwhm.
• Enabled sharpening in both tofu preprocess and tofu reco.
• Reused the phase-retrieval Fourier-domain stage when phase retrieval is active, inserting sharpening before the existing inverse FFT to avoid an extra FFT/IFFT pair.
• Added a standalone 2D FFT -> sharpen -> IFFT stage when sharpening is used without phase retrieval.
• Documented the sharpening options in the preprocessing usage docs.

Disclaimer

Parts of this PR were AI-generated.