[FEATURE] Add dedicated backend README and environment configuration guide #63

Feature Description

Introduce a dedicated README for the backend along with a .env.example file
to clearly document backend setup, configuration, and usage.

Problem Statement

Currently, there is no centralized documentation explaining how to configure
and run the backend locally. New contributors must inspect the code to infer
environment variables, database configuration, and startup commands, which
slows onboarding and increases the chance of setup errors.

Proposed Solution

• Add a backend/README.md containing:

  • Prerequisites
  • Dependency installation steps
  • Environment setup instructions
  • Backend start command
  • Basic API or health-check example

• Add a .env.example file listing all required environment variables
  with placeholder values and comments.

Component

Backend

Alternative Solutions

• A single root-level README with a backend section could partially help,
  but a dedicated backend README would be more scalable and contributor-friendly.

Additional Context