Remove PROD_URL from shared folder and use environment variables instead

[justin-phxm]

Currently, PROD_URL is hardcoded in the shared folder. To improve configuration management and security, replace all instances of the PROD_URL constant with an environment variable. Ensure that the variable is loaded from an .env file and referenced throughout the codebase using process environment access (e.g., process.env.PROD_URL).

Additionally:

• Add the PROD_URL variable to the .env.example file with a placeholder value to guide developers.
• Update all relevant documentation and setup instructions if necessary to reflect the requirement to set PROD_URL in the environment.

Acceptance Criteria:

• PROD_URL is no longer present in the codebase as a hardcoded value.
• All references use the environment variable.
• .env.example contains a commented line for PROD_URL.