Rebuild Backend on Supabase & Firebase

I have a fully-functioning React + Tailwind application that was generated with the Base44 AI builder. At the moment the code base is locked to their shared servers, so I can only extract the frontend and the TypeScript / JavaScript functions that currently run on a Deno runtime. I need a fresh, independent backend that lives entirely on my own Google infrastructure.

The goal is to recreate every backend capability—user authentication, data storage & retrieval, and all server-side processing—inside a Supabase project, while using my existing Google Cloud Storage bucket for file assets. Both Supabase and the bucket are already provisioned in the Montréal (northamerica-northeast1) region; I simply need them wired together and tied back to the React frontend.

Key points to cover
• Database: design the schema in Supabase (PostgreSQL) with row-level security and Supabase Auth. Core roles are Admin, Accountant, Employer, and Employee, each with the appropriate permissions.
• Functions: migrate or rewrite the current TypeScript/JavaScript logic as Supabase Edge Functions (Deno) or Firebase Cloud Functions—whichever best fits—so that everything runs in the same region for minimal latency.
• Storage: connect the Google Cloud Storage bucket to the app and expose signed URLs or direct links as needed.
• Frontend hookup: update environment variables, Supabase client calls, and any storage endpoints so the React code talks seamlessly to the new backend.
• Deployment & CI/CD: produce clear steps (or scripts) for staging and production deploys on Google servers.
• Documentation: short README covering database tables, RLS policies, API routes, and how each user role should interact with the system.

I already have full access to the Google Cloud console and the blank Supabase project, so you can dive straight into architecture and implementation without waiting on credentials.