docs: added project README

[Tech-Psycho95]

Summary

This PR adds an initial README.md for the ph-ee-operations-web-react project, which currently has no documentation.

The README is based entirely on the DMP 2026 project scope, the existing Angular Operations App, and the broader PH-EE ecosystem documentation.

What's Included

• Project overview — what PH-EE is, what this UI does, and who it targets (GovStack, DFSPs, G2P/P2G/Voucher orchestration)
• Tech stack — React 18+, ShadCN/UI, Tailwind CSS, Vite, Keycloak, React Router, Recharts, Axios
• Prerequisites — Node.js, npm/yarn, PH-EE backend, Keycloak
• Getting started — clone, install, environment variables, dev server
• Proposed project structure — folder layout aligned with the planned architecture
• Planned MVP features — based on the DMP 2026 issue scope
• Contributing guide — branch naming, commit conventions, code style, PR process
• Reference links — existing Angular app, PH-EE docs, GovStack wireframes, Mifos community channels

Notes

• The project structure and environment variable names are proposed defaults for a Vite + React + ShadCN setup and can be adjusted as the project takes shape.
• Keycloak realm and client ID are marked as placeholders since the actual values depend on the deployment configuration.
• Also includes a minimal .env.example for contributors to get started quickly.

Related Issue

Contributes to #2