Search in E2EE rooms does not stem despite seshat stemming functionality

### Your use case

A user searching for a singular ("book") will get results that include the plural ("books") using server-side FTS search in an unencrypted room.

The same search in an encrypted room on Element Desktop (sechat) does not return plurals.

It appears that Element is attempting to leverage sechat stemming (per [this line](https://github.com/matrix-org/seshat/blob/fdcd126a4faf05ae29db9883203c288d6611b5ff/src/index/mod.rs#L427) of code) but it's not working. Searches for "book" do not return "books," "booking," etc.

There is an open bug in seshat but the repo seems nearly dead -- last commit to main was about half a year ago.

Hoping someone on the Element side can take a look at this and see if there is a simple fix to properly use seshat stemming.

This is related to https://github.com/vector-im/element-meta/issues/1479 and https://github.com/vector-im/element-web/issues/14018.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

Start with the seshat stemming reference at src/index/mod.rs#L427 and compare it with the Element Desktop search behavior described here. Reproduce searches for “book” and verify whether encrypted-room results include “books” and “booking”; use the related issues for context before deciding what is actionable on the Element side.

Written by the indexing model from the issue text.