Fixes: #14

Summary

• Add per-node-type label column selectors in the sidebar
• Send stringified node properties from the Rust backend so the UI can switch labels without re-querying
• Apply selected display columns to Sigma labels, force-graph tooltips, search results, and cluster naming samples
• Keep the automatic display-name fallback for node types without an explicit selection

Validation

• Deferred to CI per request

Notes

• The existing local cargo test blocker remains unrelated: the local lbug C header/API is mismatched, with lbug_connection_create_arrow_rel_table_csr expecting 11 args while the Rust crate calls 12.