Remove local analysis files from repo and fix REUSE compliance

Add NL_plants_comparison.xlsx, powerplants_custom.csv, and .claude/
to .gitignore. These are local working files not needed in the upstream
repository. Fixes pre-commit reuse lint failure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MaykThewessen

.gitignore

@@ -102,3 +102,10 @@ uv.lock
 
 # jupyter
 *.ipynb
+
+# claude
+.claude/
+
+# local analysis files
+NL_plants_comparison.xlsx
+powerplants_custom.csv