Separate environment configuration into .env file

[SongChiYoung]

Description:

Currently, environment-specific settings (e.g. ports, base URLs) are likely hardcoded or scattered across the codebase.

To improve maintainability, security, and deployment flexibility, we should migrate these configurations into a dedicated .env file and load them using python-dotenv or equivalent.

Tasks:
• Create a .env file template (.env.example)
• Load environment variables using dotenv in application entrypoint
• Replace hardcoded configs (e.g. PORT, etc.)
• Update README with instructions on using the .env file

This will simplify local development and cloud deployment setups.

[SongChiYoung]

I will build it with python-dotenv