refactor: restructure project as a monorepo and implement backend API

Optimize security, efficiency, and code quality across backend and frontend

perf(backend): implement in-memory user caching to decrease db queries; improve parameter sanitization

feat(backend): integrate Groq API for routine recommendations

Optimize security, testing, and accessibility metrics to reach 90+ score

Implement welcome AuthScreen, session loader, and dynamic log out actions

Initial commit - full dynamic Firestore carbon accounting dashboard