Add CHANGELOG.md (v1.0 entry)

Initial changelog for this dataset.
v1.0 — 2025-09-14: initial public release (PDF, README, LICENSE, CITATION.cff, references.bib).
Future updates (figures, CSV, new versions) will be tracked here.

CHANGELOG.md

@@ -0,0 +1,11 @@
+# Changelog
+All notable changes to this dataset and associated records are documented here.
+
+## v1.0 — 2025-09-14
+- Initial public release
+- Added files:
+  - `AI_Visibility_Retrieval_Dynamics_White_Paper_v1.0.pdf`
+  - `README.md`
+  - `LICENSE.txt` (CC BY 4.0)
+  - `CITATION.cff`
+  - `references.bib`