Add noncommercial licensing and Stage 2 snapshot

CHECKPOINT_LICENSE.md

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+# Checkpoint and Artifact License
+
+Model checkpoints, generated samples, metrics, and other non-code artifacts in
+this project are released under:
+
+```text
+Creative Commons Attribution-NonCommercial 4.0 International
+SPDX identifier: CC-BY-NC-4.0
+URL: https://creativecommons.org/licenses/by-nc/4.0/
+```
+
+This permits non-commercial research, study, redistribution, and adaptation
+under the terms of CC BY-NC 4.0.
+
+Commercial use is not permitted without separate written permission. This
+includes, but is not limited to:
+
+- selling the checkpoints or derivative checkpoints
+- providing hosted inference as a paid or commercial service
+- integrating the checkpoints into commercial products
+- using the checkpoints for commercial production workflows
+
+The source code is licensed separately under the PolyForm Noncommercial License
+1.0.0. See [LICENSE](LICENSE).
+
+Training data is not redistributed in this repository or the Hugging Face Hub
+repository. Users are responsible for reviewing and complying with the licenses
+of any datasets they download or use.