Support annotations

### Describe your improvement idea or feature request

a Taskwarrior task can have any number of annotations, and it's great to be able to associate notes on a task, beyond the description. This feature request is to extend that functionality to taskwarrior-flutter.

### How would you like to see it implemented?

1. expose an annotation field in the task details view, with a button for New Annotation.
2. If the task has annotations, display each one at the bottom of the task details view.
3. on clicking New Annotation button, or existing annotation, open in a simple edit window (markdown supported?)
4. sync tasks with annotations, as usual.

### Put here any screenshots or videos (optional)

screenshots to follow

### How can we contact you (optional)

_No response_

### Would you like to work on this issue?

None

### By submitting this issue, I have confirmed that:

- [X] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.

Start at the task details view and task synchronization flow, then inspect how task fields are represented. Add annotation display and editing through the requested New Annotation and existing-annotation entry points, and ensure annotations sync with tasks. Done means tasks can show, create, and edit annotations while preserving synchronization.

Written by the indexing model from the issue text.