feat(graph): support unbounded visualizer snapshots

[jack-arturo]

Summary

• allow the graph snapshot endpoint to treat limit=0 as "return all" and raise the upper cap for large visualizer sessions
• include archive_threshold in graph metadata so the viewer can mirror archive handling client-side

Test plan

• pre-commit hooks passed during commit
• verify the graph visualizer can request limit=0
• verify archive threshold metadata is consumed in the visualizer

Made with Cursor

[Copilot]

Pull request overview

This PR updates the graph visualization API to better support large graph visualizer sessions by allowing clients to request an unbounded snapshot (limit=0) and by exposing consolidation archive behavior to the client via metadata.

Changes:

• Treat limit=0 on GET /graph/snapshot as “return all”, and raise the cap for bounded requests (up to 50,000).
• Add archive_threshold to the meta payload for both snapshot and stats endpoints.