Filtering of root contexts in the UI

[jas-ho]

I often have a lot of failed runs and would like to just filter the corresponding root contexts out in the UI.

Thoughts on implementation:

• simplest would be a toggle to hide failed runs
• more flexible and maybe even more useful would be some kind of filter expression textbox; this could then also allow to hide, e.g., all runs which have less than 5 turns or where the negotiation ended without consensus etc

could be related to #37 but is probably a separate issue implementation-wise

[jas-ho]

for inspiration, see e.g., the API for searching/filtering experiment runs in MLFlow https://mlflow.org/docs/latest/search-runs.html#example-expressions