fix: pass NGC API key to local NIM

[rmkraus]

Summary

• pass NGC_API_KEY into the local llm-nim Compose service, falling back to NVIDIA_API_KEY for existing .env files
• update the setup notebook generator so regenerated docker-compose.dev.yaml keeps the NGC_API_KEY wiring
• update local setup .env handling to write NGC_API_KEY alongside NVIDIA_API_KEY
• clear notebook outputs before committing

Verification

• python3 -m json.tool notebooks/setup/complete_setup_guide.ipynb
• parsed every notebook code cell with ast.parse
• verified all notebook outputs/execution counts are cleared
• docker compose -f deploy/compose/docker-compose.dev.yaml config
• verified Compose fallback renders NGC_API_KEY from NVIDIA_API_KEY with synthetic keys
• verified explicit NGC_API_KEY wins with synthetic keys
• git diff --check

Closes #31