Consolidate legacy DraggableList with `@atlaskit/pragmatic-drag-and-drop`

## Recommendation

### 🔀 CONSOLIDATE: Migrate to Pragmatic DnD

A ~300-line legacy DOM drag-and-drop script (`DraggableList`) coexists with `@atlaskit/pragmatic-drag-and-drop` across 6 consumers.

## What Was Found

- **Legacy**: Custom `DraggableList` — raw DOM event handlers, custom drag logic
- **Modern**: `@atlaskit/pragmatic-drag-and-drop` — maintained library, accessibility built-in
- 6 consumers still using the legacy implementation

## How to Fix

1. Identify consumers of `DraggableList`
2. Migrate each to use `@atlaskit/pragmatic-drag-and-drop`
3. Remove the legacy script

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**Category:** Conflicting Systems | **Priority:** Recommended | **Effort:** Medium
Part of #11022
_Filed by repo-audit skill_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11066-Consolidate-legacy-DraggableList-with-atlaskit-pragmatic-drag-and-drop-33e6d73d3650810d9d43eee8dbab215a) by [Unito](https://www.unito.io)