Use CSR-backed Sigma graph rendering

[adsharma]

Summary

• Route Sigma rendering through IcebugSigmaGraph with CSR buffers instead of per-node/per-edge mutation.
• Add CSR arrays to the Tauri graph payload and carry tableId, rowid, and optional community on nodes for backend analytics.
• Use the hosted Ladybug-Memory/icebug-rust bindings to run Leiden over an undirected CSR graph and return hierarchical clusterLevels.
• Add cluster UI controls for selecting a hierarchy level, coloring by membership, and collapsing to aggregate supernodes.
• Enable lbug Arrow support and update the lockfile to the revision exposing query_as_arrow().csr().

Validation

• npm run lint
• npm run build:frontend
• CC=/opt/homebrew/opt/llvm/bin/clang CXX=/opt/homebrew/opt/llvm/bin/clang++ cargo check