Format the Parallel n8n source consistently

[georgeatparallel]

What changed

• Ran Prettier across the TypeScript source using the repository's existing settings.
• Added a small ignore file for generated files, dependencies, caches, and the lockfile.
• Added a formatting check to CI and the publish workflow.
• Added the formatting command to the README and contributing guide.

Why

PR #14 contains the actual API and behavior changes. Keeping formatting here makes that PR easier to review and makes this one mechanical: it changes how the code is laid out, not what the node does.

This PR is stacked on #14 and should be merged after #14. Once #14 lands, its base can be changed to main.

Checks run

• Prettier check
• n8n strict lint
• TypeScript typecheck
• 12 automated tests
• Clean package installation and loading
• Production dependency audit with zero vulnerabilities