Remove leftover Nx tooling (nx.json, workspace.json, project.json)

[alphacrack]

nx.json, workspace.json, and project.json are left over from a pre-refactor monorepo setup. No npm script or workflow references Nx anymore, but the nx-related devDependencies still get installed and Dependabot keeps proposing bumps for a tool we don't use (see PR #12).

What to do

• Delete nx.json, workspace.json, project.json.
• Remove the Nx-related devDependencies from package.json (check for nx and any @nrwl/* packages).
• Close PR chore(deps-dev): bump nx from 19.8.4 to 23.1.0 #12 as no longer applicable.

Acceptance criteria

• npm ci && npm test && npm run build all pass with the Nx files and deps gone.