Improve Node.js detection to respect packageManager field

[google-labs-jules]

Modified src/detectors/node.rs to include the packageManager field from package.json in the detection logic. This ensures that the correct package manager is detected even if lockfiles are missing or if there are conflicts, prioritizing the explicitly defined manager in package.json. Added tests to verify this behavior.

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PR created automatically by Jules for task 1236752299196368220 started by @insign

[google-labs-jules]

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[insign]

Testes falharam. Revise mais profundamente.