fix: Tab draggable from full area including padding

[Copilot]

Tabs in TabView could not be drag-reordered from their padding area — only the inner content region responded to drag gestures, despite the full tab area being clickable.

Root cause: ReorderableDragStartListener was placed as the child of the Container (inside the padding), so pointer events landing in the padding were consumed by the Container without reaching the listener.

Fix (tab.dart): Moved ReorderableDragStartListener to wrap the entire Container (including its padding) rather than its interior content:

Before: FocusBorder > Container (padding) > ReorderableDragStartListener > ClipRect > content
After:  FocusBorder > ReorderableDragStartListener > Container (padding) > ClipRect > content

Original prompt

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This section details on the original issue you should resolve

<issue_title>🐛 Tab is not draggable in its padding area</issue_title>
<issue_description>Describe the bug
The red padding area of a tab in the screenshot is not draggable to reorder the tab. Only the inner part of the tab is draggable. This is unexpected and doesn't match the interactive area that makes you able to click on a tab (whole area, including the red part).

To Reproduce
Steps to reproduce the behavior:

1. Grab and try to drag a tab in the red area (padding) of a tab.
2. You can click to make the tab active there, but not grab and reorder it.

The issue is reproduceable in the Tab example in the official docs https://bdlukaa.github.io/fluent_ui/

Expected behavior
If you can hover and click in the red padding area to navigate to the tab, you should also be able to use this area to grab and drag to reorder the tab.

Screenshots

</issue_description>

<agent_instructions>Update the changelog at the end.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes 🐛 Tab is not draggable in its padding area #1307

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