ngrams: disable with proximity query

The "neighbouring words" visualisation should be disabled if the user makes a proximity query. It's not supported for those queries (nor will it be, it would be too ambiguous).

Locate the proximity-query handling and the "neighbouring words" visualisation entry point, then trace how the query type controls whether that visualisation is offered. Verify that proximity queries no longer expose the visualisation while other queries retain it, and run the relevant existing test suite if one is identified.

Written by the indexing model from the issue text.