[FEATURE]: add config parameter MAX_CONCURRENT_PIPELINES

Is your feature request related to a problem? Please describe.

As discussed here https://github.com/KeygraphHQ/shannon/discussions/508 currently the project hard coded: const MAX_CONCURRENT_PIPELINES = 5;

which may overloads local LLM, causing OOM or crashes.

Please make that setting configurable via flag or environment variable, so we can run pipelines sequentially.

Describe the solution you'd like

Please make that setting configurable via flag or environment variable, so we can run pipelines sequentially.

Which CLI mode does this apply to?

Both

Describe alternatives you've considered

No response

Additional context

No response