UI rework: per-row actions, drop sidebar

Replace the sidebar + hero + single big-button layout with a flat list of
per-version cards. Each card carries its own action button:
- Installed: ▶ Lancer (green, primary)
- Available on server only: ⬇ Installer (blue, accent) + lighter blue card
- Busy: inline mini progress bar with %, card tinted green

Each card also exposes a "..." menu (left-click opens it) with:
- Voir les release notes (works for installed and remote-only versions)
- Ouvrir le dossier (installed only)
- Supprimer cette version (installed only, with confirmation dialog)

VersionRowViewModel owns its state (InstalledIdle / AvailableIdle /
Downloading / Installing / Uninstalling) and its commands; MainViewModel
wires per-row handlers after instantiation so the row VM stays UI-only
and the services live one layer up.

ReleaseNotesViewerDialog: separate dialog reused by the menu — same
Markdown rendering as UpdateAvailableDialog but no download CTA.

Theme: AccentButton + IconButton + dark ContextMenu/MenuItem styles.

Behavior changes:
- The single global SelectedVersion + AvailableUpdate are gone; each row
  is independently actionable.
- The list now merges installed + remote: a version present on the
  server but not locally appears as a "remote-only" row, and vice-versa.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSLauncher.App/Resources/Theme.xaml

@@ -94,6 +94,77 @@
         <Setter Property="Padding" Value="14,8" />
     </Style>
 
+    <Style x:Key="AccentButton" TargetType="Button" BasedOn="{StaticResource PrimaryButton}">
+        <Setter Property="Background" Value="{StaticResource Brush.Accent}" />
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="Button">
+                    <Border x:Name="Bd"
+                            Background="{TemplateBinding Background}"
+                            CornerRadius="4"
+                            Padding="{TemplateBinding Padding}">
+                        <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center" />
+                    </Border>
+                    <ControlTemplate.Triggers>
+                        <Trigger Property="IsMouseOver" Value="True">
+                            <Setter TargetName="Bd" Property="Background" Value="{StaticResource Brush.AccentHover}" />
+                        </Trigger>
+                        <Trigger Property="IsEnabled" Value="False">
+                            <Setter TargetName="Bd" Property="Background" Value="#444" />
+                            <Setter Property="Foreground" Value="#888" />
+                        </Trigger>
+                    </ControlTemplate.Triggers>
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
+    <Style x:Key="IconButton" TargetType="Button">
+        <Setter Property="Background" Value="Transparent" />
+        <Setter Property="Foreground" Value="{StaticResource Brush.Text.Secondary}" />
+        <Setter Property="Cursor" Value="Hand" />
+        <Setter Property="Padding" Value="8,4" />
+        <Setter Property="BorderThickness" Value="0" />
+        <Setter Property="Template">
+            <Setter.Value>
+                <ControlTemplate TargetType="Button">
+                    <Border x:Name="Bd"
+                            Background="{TemplateBinding Background}"
+                            CornerRadius="4"
+                            Padding="{TemplateBinding Padding}">
+                        <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center" />
+                    </Border>
+                    <ControlTemplate.Triggers>
+                        <Trigger Property="IsMouseOver" Value="True">
+                            <Setter TargetName="Bd" Property="Background" Value="#2C2C32" />
+                            <Setter Property="Foreground" Value="{StaticResource Brush.Text.Primary}" />
+                        </Trigger>
+                    </ControlTemplate.Triggers>
+                </ControlTemplate>
+            </Setter.Value>
+        </Setter>
+    </Style>
+
+    <!-- Style ContextMenu sombre, cohérent avec le thème -->
+    <Style TargetType="ContextMenu">
+        <Setter Property="Background" Value="{StaticResource Brush.Bg.Card}" />
+        <Setter Property="BorderBrush" Value="{StaticResource Brush.Border}" />
+        <Setter Property="BorderThickness" Value="1" />
+        <Setter Property="Foreground" Value="{StaticResource Brush.Text.Primary}" />
+        <Setter Property="Padding" Value="4" />
+    </Style>
+
+    <Style TargetType="MenuItem">
+        <Setter Property="Background" Value="Transparent" />
+        <Setter Property="Foreground" Value="{StaticResource Brush.Text.Primary}" />
+        <Setter Property="Padding" Value="10,6" />
+    </Style>
+
+    <Style TargetType="Separator">
+        <Setter Property="Background" Value="{StaticResource Brush.Border}" />
+        <Setter Property="Margin" Value="4,4" />
+    </Style>
+
     <Style x:Key="VersionPill" TargetType="Border">
         <Setter Property="Background" Value="#2C2C32" />
         <Setter Property="CornerRadius" Value="12" />