feat(backdrop): Capture Window… in-app window pin (TASK 38, Good Dog ONE test)

Click-to-pin an open window as the full-bleed Live backdrop, via the existing
window:<hwnd> capture path (same render layer as game/desktop). Session-scoped:
window:/picker: keys heal to auto on reload (HWND-recycle hazard); pin wins
while the window enumerates, then auto-fallbacks (game → desktop → static); a
dead window's capture session heals to auto, no dead ends.

Fix: ScreenCaptureSourceFactory.Resolve hex-parsed "window:0x<Hwnd>" WITHOUT
stripping the 0x prefix — NumberStyles.HexNumber rejects it, so every pin
resolved null ("No capture target for this key") and the heal silently rolled
back. Same flaw in IsAliveWindowPin (pin-wins guard was dead). Both fixed.

Commit also carries an out-of-scope prerequisite: PillRadioTests.cs:105 had a
committed stray token ("...PrimaryStartButtonLabel soil;", CS1003) blocking the
whole test-project compile — token removed.

Plus the previous session's uncommitted pricing docs (one-time $29/$49) that
share TASKS.md/ai.md/HANDOFF.md.

Controls/PreviewPane.xaml

@@ -35,6 +35,20 @@
                                                 </Style>
                                             </MenuItem.ItemContainerStyle>
                                         </MenuItem>
+                                        <MenuItem Header="Capture Window…"
+                                                  Visibility="{Binding CanChangeBackground, Converter={StaticResource BoolToVis}}"
+                                                  ItemsSource="{Binding OpenWindows}">
+                                            <MenuItem.ItemContainerStyle>
+                                                <Style TargetType="MenuItem">
+                                                    <Setter Property="Header" Value="{Binding Label}"/>
+                                                    <Setter Property="Command"
+                                                            Value="{Binding DataContext.CaptureWindowCommand, RelativeSource={RelativeSource AncestorType=ContextMenu}}"/>
+                                                    <Setter Property="CommandParameter" Value="{Binding}"/>
+                                                </Style>
+                                            </MenuItem.ItemContainerStyle>
+                                        </MenuItem>
+                                        <MenuItem Header="Refresh Window List" Command="{Binding RefreshWindowsCommand}"
+                                                  Visibility="{Binding CanChangeBackground, Converter={StaticResource BoolToVis}}"/>
                                         <MenuItem Header="Refresh Desktop" Command="{Binding RefreshCaptureCommand}"
                                                   Visibility="{Binding CanChangeBackground, Converter={StaticResource BoolToVis}}"/>
                                     </ContextMenu>