feat: add task comments support, move save from fab to app bar

[13rac1]

Add ability to view, create, edit, and delete comments on tasks. My intention is to create a minimum implementation of the feature to reduce code review time. I'd like to see comments on the task preview too, but that can happen later.

Changes:

• New TaskComment entity and DTO with JSON serialization
• TaskCommentDataSource for API communication (GET/PUT/POST/DELETE)
• TaskCommentRepository interface and implementation
• TaskCommentsController for state management (Riverpod with code generation)
• TaskComments widget displaying comments with HTML rendering
• Comments section added to task edit page
• Move save button from FAB to app bar to avoid overlap with comment input - This is a UX change. I tried to avoid it to reduce the changeset and avoid the distraction, but nothing else makes sense. I'm open to other options.
• Add TaskCommentDto tests for JSON parsing

Notice: This code was primarily generated by Claude Code, but I have reviewed and tested it; it's mostly simple CRUD. There's multiple "nice to haves" which could be implemented, but nothing seems like a blocker to me. Please feel free to rip it apart!

Fixes #115

[RXTX4816]

Hi Cool Feature! I tested it and it works very good.

I did not review the code, but have some notes regarding the UI/UX design:

With your proposed design, from UX perspective, the User could mistakenly save his input instead of deleting it, when the buttons are that close next to each other and saving has no confirmation.

Previously, with the Save Button in the bottom right, and e.g. having Attachements in a Task and Editing it, the Download Button also overlaps with the Save Button. But since "Scrolling Down" shows like half the screen of empty space, this is a good workaround. In your solution, when scrolling to the bottom, one cannot scroll into empty space, so it definetly makes sense to have the Save Button moved. It should be discussed how such a UX decision is handled.

Empty Space Example Screenshot

I think the "scrolling into empty space" solution is better from a UX perspective and for less thumb-stretching, but lets see what the others have to say 😃