Refactor hardcoded Execution Engine URL to use environment configuration

[avinxshKD]

I noticed that the Execution Engine URL http://127.0.0.1:5000 is hardcoded in multiple places, specifically in src/graph-builder/graph-core/6-server.js and src/component/modals/ContributeDetails.jsx.

This makes it impossible to configure the execution backend for different environments (staging, production, or remote dev) without modifying the source code.

Proposed Sol to this: We should extract this base URL into src/serverCon/config.js (or a similar config module) and allow it to be configured via environment variables (e.g., process.env.REACT_APP_EXECUTION_ENGINE_URL), falling back to localhost only for development.

Acceptance Criteria:

• No direct references to http://127.0.0.1:5000 in the codebase.

• The URL is configurable via .env.

• Existing functionality (Compare, Run, Debug, Contribute) continues to work locally.

[avinxshKD]

@pradeeban ready to raise a Pr if this makes sense. Thanks

[pradeeban]

Sure. If an environment variable does not exist, can you make it default to the current value that is used?

[avinxshKD]

@pradeeban sure took care of it, pls verify and let me know if any chnages needed sir thanks