Ignore DLR-F25 dataset files

DLR provides the DLR-F25 under terms that forbid redistribution. These
rules were present in the working tree but never committed, so a fresh
clone did not carry the protection.

Author: Kugel-Blitz-13

.gitignore

@@ -217,3 +217,11 @@ __marimo__/
 
 # Local SSE smoke test outputs
 export.sse.json
+
+# Restricted dataset: DLR-F25 is provided by DLR under terms that forbid
+# redistribution. Never commit these files to any repository.
+DLR-F25*
+DLR_F25*
+dlr_f25*
+dlrf25*
+*F25*.xml