Added archive export ignores for theme packages

Added package-level `.gitattributes` files so subtree-published theme repositories omit agent docs and workspace metadata from GitHub-generated source archives. This keeps the files available in source checkouts while preventing `archive/main.zip` downloads from including `AGENTS.md`, `CLAUDE.md`, or `pnpm-workspace.yaml`.

Author: aileen

.gitattributes

@@ -0,0 +1,4 @@
+/AGENTS.md export-ignore
+/CLAUDE.md export-ignore
+/pnpm-workspace.yaml export-ignore
+/.gitattributes export-ignore