Add missing export-ignore entries to .gitattributes

Add .editorconfig, CLAUDE.md, and phpstan-baseline.neon to the
export-ignore list so they are excluded from distribution archives.
These files are only needed for development and should not be shipped
to end users.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: 2 people

.gitattributes

@@ -3,8 +3,11 @@
 .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
+phpstan-baseline.neon export-ignore
 phpunit.xml export-ignore