Add missing export-ignore entries to .gitattributes

Add .editorconfig and CLAUDE.md to export-ignore so they are excluded
from the distributed archive. These files are only needed for
development and should not be shipped to end users.

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

Author: 2 people

.gitattributes

@@ -3,8 +3,10 @@
 .github export-ignore
 tests export-ignore
 tmp export-ignore
+.editorconfig export-ignore
 .gitattributes export-ignore
 .gitignore export-ignore
+CLAUDE.md export-ignore
 Makefile export-ignore
 phpstan.neon export-ignore
 phpunit.xml export-ignore