Migrate from Firebase (deprecated free tier) to Supabase

[CodeVoyager15]

Description
Firebase stopped offering its free plan, so we need to move the project to Supabase for continued backend services.

Tasks

• Replace Firebase Auth with Supabase Auth
• Move Firestore data to Supabase Postgres
• Update file storage from Firebase Storage to Supabase Storage
• Update environment variables and configs
• Test all APIs and client integrations

Expected Result
All current functionality (auth, database, storage) works the same with Supabase, no downtime.

Additional Context
Supabase offers an open-source Postgres backend with auth, storage, and APIs, which should cover everything Firebase was handling.

[yrmuai]

I will work on this issue