Subtask Support Implementation

[plaintool]

Requested by: JJK (jjkerneis@free.fr)

Requirements

1. Tree Building

   • Build the task tree structure based on indentation levels parsed from the file.

2. Collapse/Expand Functionality

   • Add controls to collapse/expand task levels.
   • Collapsed tasks should be hidden from the view.

3. Task Movement Rules

   • Moving nested tasks up/down is allowed only within the same level.
   • All subtasks must move together with the parent.
   • When tasks are moved to another group, their nesting level must be recalculated relative to the root of the target group.

Notes

• Must maintain full compatibility with the existing file format and task operations.
• The feature enhances task hierarchy management and visibility.