Support Undo/Redo for Multi-Task Operations

[dlau72]

Currently, the undo/redo system only tracks single-task operations (e.g., add, edit, done, rm). However, some commands affect multiple tasks at once and are not yet covered by undo/redo. This creates inconsistencies and can lead to accidental data loss when performing bulk updates.

Examples of multi-task operations:

• done-all: marking several tasks complete in one command
• clear --completed: removing all completed tasks
• clear --active: removing all active tasks

Expected Behavior

• Any bulk operation should be recorded in history with the before/after states of all affected tasks.
• undo should restore tasks to their previous state (e.g., reactivate tasks after a done-all, restore removed tasks after a clear).
• redo should reapply the bulk change consistently.

[dlau72]

@Valentin-v-Todorov Please assign me to this issue