Add CPC update site

[Jay2owe]

Summary

• Add the Centre-Particle Coincidence (CPC) update site to sites.yml.
• Explain CPC as an ImageJ/Fiji plugin for object-based colocalization of segmented objects.
• Describe the centroid-in-object coincidence rule, the reciprocal contains relationship, regex-based image search/grouping for batch operations, and multi-target colocalization summaries across 2-5 channels.
• Link the entry to the CPC GitHub repository and maintainer.

Testing

• python -m yamllint -d relaxed -d "{rules: {key-duplicates: {}}}" sites.yml
• Duplicate ID check from .github/build.sh
• Alphabetical ordering check from .github/build.sh
• PYTHONUTF8=1 python generate-legacy-pages.py
• python -m cram --shell "C:\Program Files\Git\bin\bash.exe" tests

[ctrueden]

@Jay2owe Thanks!