Add README.md documentation to all AliceVision modules

[Copilot]

Description

Each module under src/aliceVision previously lacked inline documentation. This PR adds a README.md to every module that was missing one, following the style established by camera/ and feature/.

Features list

• Add README.md to 31 modules: calibration, cmdline, colorHarmonization, dataio, depthMap, featureEngine, fuseCut, gpu, graph, hdr, imageMasking, imageMatching, imageProcessing, lensCorrectionProfile, lightingEstimation, matchingImageCollection, mesh, mvsData, mvsUtils, panorama, photometricStereo, python, segmentation, sensorDB, sfmDataIO, sfmMvsUtils, sphereDetection, stl, system, utils, voctree

Implementation remarks

Each README covers:

• Purpose/overview of the module in the reconstruction pipeline
• Key classes and their roles (derived from header file documentation)
• Code examples where the API warrants illustration
• References to relevant papers where the algorithm has a published basis (e.g. Debevec CRF, Nistér vocabulary tree, Labatut graph-cut)

Existing READMEs (camera, feature, geometry, image, keyframe, linearProgramming, matching, multiview, numeric, robustEstimation, sfm, sfmData, track) were left unchanged.

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