Restore service experiment source tree

[unityequilibrium]

Summary

• restore the services_and_experiments source tree from local work into main as a source-only recovery PR
• add a root README that labels the folder as experimental service/prototype code
• add .gitignore coverage for service experiment build output, target directories, binaries, caches, and local env files

Excluded from recovery

• local .env files
• uet_build/debug cache
• uet_miner/target_gpu_win
• compiled binaries such as .exe and uet_miner_linux
• generated uet_core Cargo.lock from local smoke testing

Verification

• ran git add dry-run to inspect tracked files
• scanned staged files for env/binary/build/cache path leaks
• ran git diff --cached --check after mechanical whitespace cleanup
• ran cargo check --manifest-path services_and_experiments/uet_core/Cargo.toml (passes with warnings only)

[unityequilibrium]

Superseded by #10, which includes the services source recovery plus the rest of the local workspace batch under the Source+Manifest policy.