Convert Windows App to Node.js Web

I have a Windows-only program that performs intensive text-based data processing. It ingests large text files, runs a series of transformations and validations, then presents the results in a simple desktop UI. I now need the same workflow available in any modern browser, built with Node.js on the back end.

The existing logic is well-structured and written in C#; I can provide the full source, sample data sets, and a short functional spec that explains each processing step. Your task is to port the core algorithms, recreate the current screens as responsive web pages, and ensure the output matches the desktop version byte-for-byte.

You are free to choose frameworks that fit the Node.js ecosystem—Express or Fastify for routing, a templating engine or React/Vue for the front end, and any lightweight store (SQLite, Postgres, Mongo) to hold intermediate results. Performance is important: the new service should handle the same volume of text without noticeable slowdown.

Deliverables:
• Complete Node.js codebase with clear folder structure
• Equivalent text-processing modules fully tested (unit + integration)
• Front-end pages mirroring existing UI/UX
• Deployment script or Dockerfile so I can spin it up on a fresh server
• Brief setup guide and API docs

I will perform side-by-side testing with the Windows app; acceptance is met when both versions return identical results on the provided sample files and the web UI remains responsive during processing.