Add a Behavior preference to disable the emoji autocomplete picker
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### Description
When typing colons at the end of French sentences like:
```
Et voilà :
```
The emoji picker pops up. Users who don't use emoji find this disruptive, and it interferes with natural typing in languages where colons are preceded by a non-breakable space.
### Proposal
Add a user preference toggle under **User Settings \> Preferences \> Behavior** to disable the emoji autocomplete picker.
- Default: Enabled (preserving current behavior for existing users)
- When disabled: The emoji autocomplete picker will not appear when typing `:` in text fields
- Users can still insert emoji via other means (e.g., the emoji button in the toolbar, copy-paste)
#### Additional Considerations
* [ ] ~documentation will need to be updated to reflect the new preference option
* [ ] A release post item will be needed to announce this change
* [ ] We will need to track this behaviour (e.g., via usage tracking / internal analytics) to understand adoption and validate the decision
issue