Fix Sequence Editor TreeView selection visibility after modifications

[Copilot]

TreeView selection highlighting disappears when exports are modified or packages are saved, making it impossible to determine the current sequence in files with duplicate sequence names.

Root Cause

When modifications occur, LoadSequences() disposes all TreeViewEntry objects and creates new ones. TreeViewHelper only syncs the binding passively—it doesn't restore the IsSelected property on the new objects.

Changes

• Replace TreeViewHelper with NodeTreeSelectionBehavior in SequenceEditorWPF.xaml
• NodeTreeSelectionBehavior actively manages IsSelected state during selection changes

- <peregrineTreeView:TreeViewHelper BoundSelectedItem="{Binding SelectedItem}" />
+ <peregrineTreeView:NodeTreeSelectionBehavior SelectedItem="{Binding SelectedItem}" />

This matches PackageEditor's implementation, which already switched from TreeViewHelper to NodeTreeSelectionBehavior to solve the same issue (commented-out code still visible in PackageEditorWindow.xaml).

Original prompt

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This section details on the original issue you should resolve

<issue_title>Sequence Editor - very difficult to determine current sequence on modification/save</issue_title>
<issue_description># Please fill out the following form in its entirety.
The more information you provide, the easier it will be for us to reproduce the issue.

Describe the bug
Sequence Editor is very inconsistent in dispalying the current selected sequence. It often 'deselects' a sequence, which means you have no idea what sequence you are in. In files that have multiple duplicate named sequences - it makes it extremely difficult to tell which export is selected. Additionally, if a sequence is modified, you have no way to tell what is selected. This is due to how the tree view is set up in Sequence Editor's XAML file.

To Reproduce
Open Sequence Editor, any package.

For the export modification issue, simply edit an object in the sequence - such as cloning, trashing, etc.

For the unselected UI, you need to modify an export, and then save the package, so the modification layer goes away. You are then left without any selected sequence color coding. This is a very common occurrence.

Expected behavior
Tree view should behave like package editor's tree view and properly update on save and have selections visible

Screenshots and files used to replicate this
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Version information:
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Nightly

Stack trace
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Other information
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Comments on the Issue (you are @copilot in this section)

• Fixes Sequence Editor - very difficult to determine current sequence on modification/save #391

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