design: wire the sans family into the window; fonts ship as explicit Resource items

The bundled faces were packaged but unused — no style referenced FontFamily.Sans, so the app
still rendered Segoe UI. MainWindow now sets FontFamily from the token, which cascades to every
child (dialogs follow in the sweep).

Font packaging: six explicit <Resource> items instead of the Assets\Fonts\*.ttf glob, so the
guard can name exactly what must ship.

Investigation worth recording: a runtime assertion that the families resolve from
pack://application:,,,/ would have needed an Application instance inside the test host, and
without one WPF resolves the pack authority against the test host — every probe failed,
including the app icon that demonstrably works. The resources ARE embedded (the lowercase
`assets/fonts/inter-regular.ttf` entry is present in ytLive.g.resources); the assertion was
removed rather than faked, and the real confirmation is a launch, which is a visual check.

Guard remains structural: files are real binaries, each is a Resource in the csproj, the theme
uses pack URIs, notices + both OFL texts are present, and no third family sneaks in.

MainWindow.xaml

@@ -13,6 +13,7 @@
         MinWidth="1366" MinHeight="768"
         Icon="/ytLive;component/Assets/llamacasty-icon.png"
         Background="#1a1a2e"
+        FontFamily="{StaticResource FontFamily.Sans}"
         WindowStartupLocation="Manual"
         Closing="MainWindow_Closing"
         Loaded="MainWindow_Loaded"