refactor: organize socket.io request handlers into subdirectories}
- Restructure flat request handler files into categorical subdirectories:
ai/, client/, cluster/, connection/, hash-field/, key/, memory/,
monitor/, probabilistic/, redis/, search/, settings/, timeseries/,
vectorset/
- Update internal import paths in relocated handler modules to reflect
new directory structure
- Update socket.mjs to reference handlers at their new paths
- Update build.yml, README.md, artifacts/cluster.md, and package.json
with minor adjustments