Hide Completed/Show All has a bug and its fix

Hide Completed/Show All as shown in tutorial has a bug.

1. Check a task
2. Press "Hide Completed"
3. The task doesn't show
4. Press "Show all"
5. The task shows up
6. Bad, current behavior: The task checkbox is displayed unchecked, leading the user to think the task is not checked - and mismatches unchecked tasks with the pending count (by one, in this case)
7. Correct, future behavior: The task checkbox is checked

The fix lies in imports/ui/Task.html
Instead of:
``
or similar code,
Mention:
` {{#if isChecked}}

{{else}}

{{/if}}`

Start in imports/ui/Task.html, where the task checkbox is rendered. Reproduce the Hide Completed/Show All steps from the issue, then inspect how isChecked controls the checkbox state. Done means a previously checked task remains visibly checked after it is shown again and the pending count matches.

Written by the indexing model from the issue text.