fix: compile SelectorBar.xaml as a Page to prevent rare startup crash

[haoliuu]

Summary

SelectorBar.xaml was excluded from XAML compilation (<Page Remove> in the csproj) and shipped as a loose Content file. Since App.xaml merges it as a resource dictionary (<ResourceDictionary Source="/Styles/SelectorBar.xaml" />), the framework had to resolve it at runtime via ms-resource:///Files/Styles/SelectorBar.xaml. In rare cases that runtime lookup can fail at startup, throwing during App.xaml parsing and crashing the app before any UI loads.

This has been present since the app's initial release. Every other Styles/*.xaml dictionary is a compiled/embedded Page - SelectorBar was the only one on this runtime-lookup path.

Fix

Removed the <Page Remove="Styles\SelectorBar.xaml" /> so the file compiles into an embedded XBF like every other style dictionary. App.xaml now binds to the embedded compiled resource instead of a runtime file lookup, eliminating the failure mode.

Related to #61457801

Verification

• Build succeeds with 0 errors.
• Confirmed Styles\SelectorBar.xbf is now produced and embedded (listed in embed.resfiles alongside Button, ComboBox, NavigationView).
• App launches and the home page renders normally.

[Copilot]

Pull request overview

This PR fixes a rare WinUI 3 startup crash by ensuring Styles/SelectorBar.xaml is XAML-compiled (embedded XBF) like the other merged style dictionaries, avoiding a runtime resource-file lookup during App.xaml parsing.

Changes:

• Removed the project file rule that excluded Styles\SelectorBar.xaml from XAML compilation (<Page Remove=...>), allowing it to be compiled/embedded.