Add SlicerMicroView extension

[falkwiegmann]

New extension: SlicerMicroView

Reads and writes GE eXplore / MicroView micro-CT volumes in VFF format, including the GE ncaa header (voxel size from elementsize, Hounsfield calibration from water/air) and the minimal VFF headers written by reconstruction toolkits. Files open directly through Add Data; volumes can be exported back to VFF for MicroView.

Repository: https://github.com/UBC-Ford-lab/SlicerMicroView
License: MIT
Tier: 1

Tested with Slicer 5.12.3 on macOS with 1.4 GB and 2.1 GB GE eXplore CT 120 reconstructions; the module includes a self-test with synthetic files covering both header dialects, HU rescaling and writer round trips.

Checklist (tier 1):

• Extension name reasonable (prefixed with "Slicer" because it bridges Slicer and MicroView)
• Repository name is Slicer+ExtensionName
• Repository has topic 3d-slicer-extension
• Description summarizes purpose in 1-2 sentences
• No known related patents
• LICENSE in repository root, license named on homepage
• scm_url / scm_revision correct
• Icon URL is a raw-data URL
• Screenshot URL correct
• JSON consistent with top-level CMakeLists.txt
• Homepage contains name, description, image, module descriptions
• Unused GitHub features hidden
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