Resolve crop recommendation dataset source and license

[sardorcodev]

Resolve the source and license status for the crop recommendation dataset used by the MVP training workflow.

Current status:

• dataset/Crop_recommendation.csv is download-only/user-provided.
• Redistribution rights are not claimed.
• Model artifacts remain MVP/demo-only.

Scope:

• Identify a confirmed source.
• Confirm dataset license and redistribution rights.
• Compare candidate source using dataset fingerprint tooling.
• Update DATASET_CARD.md and DATA_POLICY.md.

Acceptance criteria:

• Dataset source is documented.
• License status is documented.
• Fingerprint match or mismatch is recorded.
• Model promotion gate is updated.