UX Issue: Button to move to top of upcoming tasks

**Related bugs and feature requests if any**
No related issues/bugs

**The Issue**
When users have a long task list, manually scrolling back to the top can be tedious. Adding a button to quickly scroll to the top improves navigation and usability.

**Describe the solution you'd like**
Add a floating action button (FAB) or a similar UI element that appears when the user scrolls down the task list.
The button should smoothly scroll the task list back to the top when clicked.
It should disappear when the user is already at the top of the list.
Design specifications:
The button should be minimal and consistent with the app's theme.
Consider using an upward arrow icon (Icons.arrow_upward) for the button.

Start by locating the screen that renders the upcoming task list and review how its scrolling is handled. Add the requested upward control so it appears after scrolling down, returns the list smoothly to the top when tapped, and is hidden at the top; verify the behavior on a long task list.

Written by the indexing model from the issue text.