feat: improve task reordering UX with visible drag handle

[laba74]

Add a grip icon (PhDotsSixVertical) to task items to make drag-and-drop reordering more discoverable. The handle:

• Provides clear visual affordance for dragging
• Limits drag interaction to the icon only (more intuitive)
• Shows cursor-grab on hover
• Hides during task editing mode

Also simplified code by removing redundant draggingEnabled logic.

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