design: every window inherits Inter (implicit Window style)

Dialogs are separate WPF windows, so the FontFamily set on MainWindow never reached them —
GoLive, Socials and the four pickers still rendered Segoe UI while the main window used Inter.

The theme now carries an implicit Window style (family + Display text mode + layout rounding).
Guard: DialogTypographyTests opens a real Window inside the real app and asserts it resolves the
bundled Inter family — which fails if the style or the font resource goes missing — and asserts
no dialog sets FontFamily itself, i.e. nobody opts out of the standard.

Themes/Controls.xaml

@@ -2,6 +2,16 @@
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:Helpers="clr-namespace:ytLive.Helpers">
 
+    <!-- Typography for every window: dialogs are separate WPF windows, so FontFamily set on
+         MainWindow does not reach them. This implicit style is the one place that does — a
+         dialog inherits Inter without setting anything, and the design standard holds for every
+         surface the creator can open. -->
+    <Style TargetType="Window">
+        <Setter Property="FontFamily" Value="{StaticResource FontFamily.Sans}"/>
+        <Setter Property="TextOptions.TextFormattingMode" Value="Display"/>
+        <Setter Property="UseLayoutRounding" Value="True"/>
+    </Style>
+
     <!-- Base button style -->
     <Style x:Key="YtButton" TargetType="Button">
         <Setter Property="Background" Value="{StaticResource Brush.Tertiary}"/>