Make markdown task lists interactive on Android

Is your feature request related to a problem? Please describe.

Markdown task lists (- [ ] and - [x]) are already supported in the web and desktop clients, where users can interact with them directly.

On Android, task lists are displayed correctly but cannot be toggled by tapping on the checkbox. This creates an inconsistent experience between clients and makes shared task lists less convenient to use on mobile devices.

Describe the solution you'd like

Allow users to tap on markdown task list checkboxes inside messages.

For example:

- [ ] Buy milk
- [ ] Update documentation

After tapping the first item, the message would automatically be updated to:

- [x] Buy milk
- [ ] Update documentation

This should work similarly to the existing implementation in the web and desktop clients.

Describe alternatives you've considered

n\a

Additional context

This feature already exists in other Nextcloud Talk clients. Bringing it to Android would improve feature parity and make collaborative task lists much more convenient to use on mobile devices.

Start by locating the Android message-rendering path for Markdown task lists and compare its behavior with the existing web and desktop implementations. Implement checkbox tapping so the corresponding task-list item is updated, then verify that tapping changes the message from unchecked to checked and preserves other items.