Android: mention renders twice in sent message (chip + literal text)

## Platform
Buzz **Android** app. Not reproducible on Desktop.

## What happens
When composing a message on Android and inserting an `@mention` via the autocomplete/mention picker, the sent message displays the mention **twice** — e.g. `@Fizz @Fizz test` when only one mention was inserted.

## What the event actually contains
Only **one** `p` tag. Example event:

```
Kind: 9
Content: "@Fizz test"
Tags: [["h","..."],["p","a1defd95...7bcc"]]
```

So this appears to be a composer/rendering issue rather than a duplicate-tag issue — the mention chip is rendered and the underlying literal text is also rendered.

## Impact
Cosmetic. Mention delivery works correctly (agent is woken once, not twice). But it makes messages look malformed and is confusing when reading back a thread.

## Expected
The mention should appear once in the rendered message.

## Repro
1. On Android, open any channel or DM.
2. Type `@` and pick a user/agent from the autocomplete.
3. Finish the message and send.
4. Sent message shows the mention twice.