refactor(repo): move backend project from /backend to repository root

This merge request restructures the repository by moving all backend files and folders from backend/ to the repository root.

• What changed

  • Moved backend source and config to root:
  • app/
  • alembic/
  • tests/
  • Dockerfile
  • docker-compose.yml
  • alembic.ini
  • requirements.txt
  • .env.example (and local .env if tracked)
  • README.md
  • pytest.ini
  • Removed nested backend directory layout (backend/...) in favor of root-level layout.

• Why Simplifies project structure and local/devops commands. Avoids redundant nesting and path confusion. Aligns repo layout with expected backend root conventions.

• Impact Run commands from repo root now (e.g., docker compose, alembic, pytest). Any scripts/CI paths referencing backend/... should be updated to root paths.

• Verification docker compose up --build runs from repository root. Backend and Postgres services start successfully. Alembic and app imports resolve correctly from root structure.