Exclude .pnpm-store from prettier and git

On the Gitea runner, pnpm's content-addressable store ends up inside
the workspace (.pnpm-store/) instead of the global cache location -
format:check was scanning its content-addressable blobs as if they
were source files, some of which happen to parse as JS/TS-like text
and crash prettier's parser outright rather than just wasting time.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitignore

@@ -1,5 +1,6 @@
 # dependencies
 /node_modules
+/.pnpm-store
 /.pnp
 .pnp.*
 .yarn/*