Add brevetkarte-blanko.tex to gitignore and clean target

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile

@@ -86,7 +86,7 @@ shell:
 # Clean generated files
 clean:
 	@echo "Cleaning generated files..."
-	rm -f *.aux *.log *.out *.toc *.pdf
+	rm -f *.aux *.log *.out *.toc *.pdf brevetkarte-personalized.tex brevetkarte-blanko.tex brevetkarte-rueckseite.tex
 
 # Clean everything including Docker image
 clean-all: clean