feat(app): add draggable titlebar tabs

[dbpolito]

Issue for this PR

N/A

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

• Adds drag-and-drop reordering for desktop v2 titlebar tabs.
• Persists the reordered tab list through the existing global tabs store.
• Reuses the app's existing solid-dnd sortable tab pattern from review/file tabs.
• Disables native anchor dragging on titlebar tabs so drag gestures reorder tabs instead of creating link drags.

How did you verify your code works?

• Manually started the desktop dev app with bun run dev:desktop as video below

Screenshots / recordings

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found

PR #31364: feat(app): draggable tabs
#31364

This PR appears to be directly related to the current PR #32590. Both address draggable/reorderable tabs functionality. PR #31364 has a similar title focusing on "draggable tabs" while the current PR specifically targets "draggable titlebar tabs." They may be addressing the same feature or closely related work that could result in duplicate effort or conflicts.