Add AGENTS.md and CLAUDE.md to gitattributes export-ignore

Mark AGENTS.md and CLAUDE.md files as export-ignore in .gitattributes
to exclude them from package exports, similar to other development
and documentation files.

Author: OskarStark

src/toolbox/.gitattributes

@@ -1,5 +1,7 @@
 /.gitattributes     export-ignore
 /.gitignore         export-ignore
+/AGENTS.md          export-ignore
+/CLAUDE.md          export-ignore
 /phpunit.xml.dist   export-ignore
 /phpstan.dist.neon  export-ignore
 /tests              export-ignore