Switch data licence to CDLA-Permissive-2.0 to match proposal §5.2

Data: CDLA-Permissive-2.0 (was CC BY 4.0). Code stays Apache-2.0, docs CC BY 4.0.
Updated LICENSE-DATA, NOTICE, LICENSING.md, README, and the HF dataset-card tag.

Author: KoyoAli

HF-DATASET-CARD.md

@@ -1,7 +1,7 @@
 ---
 # ==== This YAML block is what makes the dataset machine-readable. ====
 # Hugging Face generates Croissant metadata from it. Get it right.
-license: cc-by-4.0
+license: cdla-permissive-2.0
 # ISO 639-3 throughout. Nigerian Pidgin has no 639-1 code, so using 639-1 for the
 # other two would mean mixing standards across the schema, the card and the file paths.
 # Hugging Face accepts 639-3. Confirm with Eric which codes the corpus already uses.