Stop tracking build artifacts in dist/

The committed 1.0.0 wheel/tarball were checked out by the publish
workflow and re-uploaded alongside the freshly built 1.0.1 files,
causing a '400 File already exists' failure on the stale 1.0.0 wheel.
Untrack dist/ and gitignore it so only freshly built artifacts are
published.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: yanyanzhu-pnnl

.gitignore

@@ -58,3 +58,6 @@ testprojectJson/
 site/
 
 .claude
+
+# Build artifacts
+dist/