refactor: extract HealthBanner + promote converters to theme — Phase 2, Commit 13

HealthBanner.xaml takes the Row 1 YouTube-health banner (report-by-exception).

Converters: promoted the 7 value<->visibility converters (BoolToVis, Inverse,
NotNull, Null, Hidden, EnumToBool, AllTrueToVis) from MainWindow.Window.Resources
into Themes/Controls.xaml so extracted UserControls can resolve them. AGENTS rule:
controls cannot reach into a window's own named resources; they resolve from the
app-level merged theme instead. Promoted all of them (not just NotNullToVis) so
every pending extraction keeps working without window-level references.

Zero behavior change; build 0 warnings; 246 pass, only the 2 known failures.
Docs: ViewModels/index.md Phase 2 tracker updated in the same commit.

Controls/HealthBanner.xaml

@@ -0,0 +1,12 @@
+<UserControl x:Class="ytLive.Controls.HealthBanner"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <!-- YouTube health banner (TASK 5 item 3): report-by-exception — visible
+         ONLY while a warning/error configuration issue exists. Amber for
+         warning, darker red for error (HealthIssueBackground). -->
+    <Border Background="{Binding HealthIssueBackground}"
+            Visibility="{Binding HealthIssueBanner, Converter={StaticResource NotNullToVis}}">
+        <TextBlock Text="{Binding HealthIssueBanner}" Foreground="White" FontSize="13"
+                   FontWeight="SemiBold" Margin="16,8" TextTrimming="CharacterEllipsis"/>
+    </Border>
+</UserControl>

Controls/HealthBanner.xaml.cs

@@ -0,0 +1,11 @@
+using System.Windows.Controls;
+
+namespace ytLive.Controls;
+
+public partial class HealthBanner : UserControl
+{
+    public HealthBanner()
+    {
+        InitializeComponent();
+    }
+}

MainWindow.xaml

@@ -31,21 +31,6 @@
 
     <Window.Resources>
         <ResourceDictionary>
-            <BooleanToVisibilityConverter x:Key="BoolToVis"/>
-        <Helpers:InverseBoolToVisibilityConverter x:Key="InverseBoolToVis"
-                                                  xmlns:Helpers="clr-namespace:ytLive.Helpers"/>
-        <Helpers:NotNullToVisibilityConverter x:Key="NotNullToVis"
-                                              xmlns:Helpers="clr-namespace:ytLive.Helpers"/>
-        <Helpers:NullToVisibilityConverter x:Key="NullToVis"
-                                           xmlns:Helpers="clr-namespace:ytLive.Helpers"/>
-        <Helpers:HiddenBoolToVisibilityConverter x:Key="HiddenBoolToVis"
-                                                 xmlns:Helpers="clr-namespace:ytLive.Helpers"/>
-        <Helpers:EnumToBoolConverter x:Key="EnumToBool"
-                                     xmlns:Helpers="clr-namespace:ytLive.Helpers"/>
-        <Helpers:AllTrueToVisibilityConverter x:Key="AllTrueToVis"
-                                              xmlns:Helpers="clr-namespace:ytLive.Helpers"/>
-
-
 
         <!-- Red dot shown in the taskbar icon while live -->
         <DrawingImage x:Key="LiveOverlay">
@@ -207,14 +192,7 @@
         </Border>
 
         <!-- ═══ MIDDLE: Main Content ═══ -->
-        <!-- YouTube health banner (TASK 5 item 3): report-by-exception — visible
+        <controls:HealthBanner Grid.Row="1"/>
-             ONLY while a warning/error configuration issue exists. Amber for
-             warning, darker red for error (HealthIssueBackground). -->
-        <Border Grid.Row="1" Background="{Binding HealthIssueBackground}"
-                Visibility="{Binding HealthIssueBanner, Converter={StaticResource NotNullToVis}}">
-            <TextBlock Text="{Binding HealthIssueBanner}" Foreground="White" FontSize="13"
-                       FontWeight="SemiBold" Margin="16,8" TextTrimming="CharacterEllipsis"/>
-        </Border>
 
         <Grid Grid.Row="2" Margin="8">
             <Grid.RowDefinitions>

Themes/Controls.xaml

@@ -1,5 +1,6 @@
 <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
-                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+                    xmlns:Helpers="clr-namespace:ytLive.Helpers">
 
     <!-- Base button style -->
     <Style x:Key="YtButton" TargetType="Button">
@@ -631,4 +632,15 @@
         </Setter>
     </Style>
 
+    <!-- Value-to-visibility converters, promoted from MainWindow.Window.Resources
+         so extracted UserControls can resolve them (AGENTS: controls must not
+         reach into a window's own resources; they share the app-level theme). -->
+    <BooleanToVisibilityConverter x:Key="BoolToVis"/>
+    <Helpers:InverseBoolToVisibilityConverter x:Key="InverseBoolToVis"/>
+    <Helpers:NotNullToVisibilityConverter x:Key="NotNullToVis"/>
+    <Helpers:NullToVisibilityConverter x:Key="NullToVis"/>
+    <Helpers:HiddenBoolToVisibilityConverter x:Key="HiddenBoolToVis"/>
+    <Helpers:EnumToBoolConverter x:Key="EnumToBool"/>
+    <Helpers:AllTrueToVisibilityConverter x:Key="AllTrueToVis"/>
+
 </ResourceDictionary>

ViewModels/index.md

@@ -54,7 +54,8 @@ Progress (Commit N/12 · tag):
 - [x] **Phase 1 complete:** core `MainViewModel.cs` split into 10 functional partials (1,890 → 758 lines).
 
 **Phase 2 — `MainWindow.xaml` split into UserControls** (new `Controls/` folder, namespace `ytLive.Controls`):
-- [x] **Commit 12 · `refactor-commit-12`** — **BottomBar** → `Controls/BottomBar.xaml(.cs)` (gear menu + stream stats + quality dropdown; `GearButton_Click` moved to the control's code-behind). Pending: TopBar, health banner, left scene/chat panel, preview pane, overlay host.
+- [x] **Commit 12 · `refactor-commit-12`** — **BottomBar** → `Controls/BottomBar.xaml(.cs)` (gear menu + stream stats + quality dropdown; `GearButton_Click` moved to the control's code-behind).
+- [x] **Commit 13 · `refactor-commit-13`** — **HealthBanner** → `Controls/HealthBanner.xaml` (Row 1). Also promoted the 7 value↔visibility converters out of `MainWindow.Window.Resources` into `Themes/Controls.xaml` so extracted controls can resolve them (app-level, not window-level). Pending: TopBar, left scene/chat panel, preview pane, overlay host.
 
 The partial `.cs` files land next to `MainViewModel.cs` in this folder as the split
 proceeds; each partial carries its own `using`s and re-declares nothing from core.