feat(drag-and-drop): add shadowDragHandle support for Shadow DOM handle matching

[driskull]

Summary

This PR adds support for a new config option, shadowDragHandle, to enable drag handle matching inside Shadow DOM using event composedPath traversal.

What Changed

• Added shadowDragHandle to parent configuration types.
• Updated drag handle validation to:
  • Prefer shadowDragHandle when provided.
  • Match selectors against the event composedPath.
  • Skip querySelector-based matching in that mode.
• Kept existing behavior for dragHandle unchanged when shadowDragHandle is not set.
• Added end-to-end test coverage for:
  • Native drag behavior with shadow-based handles.
  • Synthetic drag behavior with shadow-based handles.
  • Negative path where dragging from non-handle areas is rejected.
  • Precedence path showing shadowDragHandle is used instead of dragHandle selector matching.
• Updated test utilities to reliably target elements in open Shadow roots and dispatch composed events where needed.

Why

Selector matching via querySelector cannot traverse into Shadow DOM internals. Matching with composedPath enables reliable drag-handle validation for web components and encapsulated UI.

Testing Notes

• Added targeted Playwright scenarios for both desktop native drag and mobile synthetic drag flows.

#170

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