Publish to npm

[ldraney]

Context

Currently the tool is only usable from a local clone. Publishing to npm enables the intended UX:

npx dev-sop-engine .

What this covers

• Pick a package name (check availability: dev-sop-engine, sop-engine, @dev-sop/engine)
• Configure package.json for publishing (main, bin, files, engines)
• Add prepublish build step
• Set up npm publish workflow (manual or on tag/release)
• README for npm listing

Depends on

• Test suite and CI (Add Pages workflow and polish landing page for launch #29 or equivalent) — don't publish without tests