docker-compose.yml hardcoded credentials

[nwosum113-ui]

Summary

Refactor Docker Compose configuration to use environment variables for Postgres credentials, improving security and flexibility.

Changes

• Replace hardcoded Postgres credentials in docker-compose.yml with environment variable placeholders
• Add .env.example file to document required environment variables
• Update service definitions to reference environment variables for credentials

Impact

• Postgres credentials are now configurable via environment variables
• Improved security by avoiding hardcoded sensitive data
• Easier credential management across different environments

closes #253

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