Add startup visual modes and attempt registry

Implement startup visual behavior, de-duplicate startup attempts, and improve failure UX.

Key changes:
- Add spec and docs for startup visuals and timing contract (.trae/specs and docs/LAUNCHER_STARTUP_VISUALS.md).
- Introduce StartupVisualPreferences contract and resolver; create SplashWindow via resolved mode.
- Add StartupAttemptRecord model and a file-backed StartupAttemptRegistry to persist and coordinate in-progress startup attempts (attach/adopt, soft/hard timeouts, IPC/connect state, lifecycle updates).
- Update LauncherFlowCoordinator to: adopt/attach to existing attempts, track IPC connection and soft/hard timeouts (30s/120s), show delayed UI state, attempt foreground recovery via public IPC, compose detailed launch result metadata, and mark registry states (soft timeout, detached waiting, succeeded, failed).
- Add TryActivateExistingInstanceAsync to attempt activating an existing desktop via IPC.
- Change failure flow: ShowFailureWindowAsync now returns user choice; ErrorWindow updated to present Activate/Wait/Open Logs/Exit semantics and new layouts/styles; improved button wiring and debug/dev mode handling.
- Add UI and resource tweaks (ErrorWindow and SplashWindow changes), project asset link for nightly logo, and unit tests for StartupVisualPreferences.

These changes prevent duplicate desktop processes during slow startups, provide clearer UX for delayed startups, and persist startup attempt state across Launcher invocations for safer recovery/attach behavior.

LanMountainDesktop.Launcher/Views/SplashWindow.axaml

@@ -3,85 +3,92 @@
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:views="clr-namespace:LanMountainDesktop.Launcher.Views"
-        xmlns:ui="using:FluentAvalonia.UI.Controls"
         mc:Ignorable="d"
-        d:DesignWidth="480"
-        d:DesignHeight="320"
         x:Class="LanMountainDesktop.Launcher.Views.SplashWindow"
         x:DataType="views:SplashWindow"
         Title="LanMountain Desktop"
         Width="480"
         Height="320"
         CanResize="False"
+        ShowInTaskbar="False"
         WindowStartupLocation="CenterScreen"
         SystemDecorations="None"
-        Background="{DynamicResource SolidBackgroundFillColorBaseBrush}"
+        Background="#0B0B0B"
         TransparencyLevelHint="None"
         Icon="/Assets/logo.ico">
   <Design.DataContext>
     <views:SplashWindow />
   </Design.DataContext>
 
-  <Grid>
-    <!-- 左上角：应用名称 -->
-    <TextBlock x:Name="AppNameText"
-               Text="LanMountain Desktop"
-               FontSize="24"
-               FontWeight="SemiBold"
-               VerticalAlignment="Top"
-               HorizontalAlignment="Left"
-               Margin="24,24,0,0"
-               Foreground="{DynamicResource TextFillColorPrimaryBrush}" />
-
-    <!-- 底部区域：进度条和状态 -->
-    <Grid VerticalAlignment="Bottom" Margin="24,0,24,24">
-      <Grid.RowDefinitions>
-        <RowDefinition Height="Auto"/>
-        <RowDefinition Height="Auto"/>
-      </Grid.RowDefinitions>
-      
-      <!-- 第一行：左下角版本信息，右下角阶段文字 -->
-      <Grid Grid.Row="0" Margin="0,0,0,8">
-        <Grid.ColumnDefinitions>
-          <ColumnDefinition Width="*"/>
-          <ColumnDefinition Width="Auto"/>
-        </Grid.ColumnDefinitions>
-        
-        <!-- 左下角：版本和开发代号 - 可点击打开开发者界面（隐藏功能） -->
-        <Border x:Name="VersionTextBorder"
-                Grid.Column="0"
-                Background="Transparent"
-                Cursor="Hand"
-                HorizontalAlignment="Left"
-                VerticalAlignment="Bottom">
-          <TextBlock x:Name="VersionText"
-                     FontSize="11"
-                     Foreground="{DynamicResource TextFillColorSecondaryBrush}"
-                     Opacity="0.8"
-                     Text="1.0.0 (Administrate)" />
-        </Border>
-        
-        <!-- 右下角：阶段文字 -->
-        <TextBlock x:Name="StatusText"
-                   Grid.Column="1"
-                   FontSize="11"
-                   Foreground="{DynamicResource TextFillColorSecondaryBrush}"
-                   HorizontalAlignment="Right"
-                   VerticalAlignment="Bottom"
-                   Opacity="0.8"
-                   Text="Initializing..." />
+  <Grid RowDefinitions="*,Auto"
+        Background="#0B0B0B">
+    <Grid Grid.Row="0">
+      <Grid x:Name="CompactHero"
+            Margin="24">
+        <TextBlock x:Name="AppNameText"
+                   Text="LanMountain Desktop"
+                   FontSize="24"
+                   FontWeight="SemiBold"
+                   VerticalAlignment="Top"
+                   HorizontalAlignment="Left"
+                   Foreground="#F6F7FB" />
+      </Grid>
+
+      <Grid x:Name="FullscreenHero"
+            IsVisible="False">
+        <StackPanel HorizontalAlignment="Center"
+                    VerticalAlignment="Center"
+                    Spacing="24">
+          <Border Width="240"
+                  Height="240"
+                  Background="Transparent">
+            <Image Source="/Assets/logo_nightly.png"
+                   Stretch="Uniform" />
+          </Border>
+
+          <TextBlock Text="LanMountain Desktop"
+                     HorizontalAlignment="Center"
+                     FontSize="26"
+                     FontWeight="SemiBold"
+                     Foreground="#F6F7FB" />
+        </StackPanel>
       </Grid>
-      
-      <!-- 底部：进度条 -->
-      <ProgressBar x:Name="ProgressIndicator"
-                   Grid.Row="1"
-                   Minimum="0"
-                   Maximum="100"
-                   Value="0"
-                   Height="4"
-                   IsIndeterminate="False"
-                   Foreground="{DynamicResource AccentFillColorDefaultBrush}"
-                   Background="{DynamicResource ControlStrokeColorDefaultBrush}" />
     </Grid>
+
+    <Border Grid.Row="1"
+            Padding="24,18,24,24"
+            Background="Transparent">
+      <Grid RowDefinitions="Auto,Auto"
+            RowSpacing="10">
+        <Grid ColumnDefinitions="*,Auto">
+          <Border x:Name="VersionTextBorder"
+                  Background="Transparent"
+                  Cursor="Hand"
+                  HorizontalAlignment="Left">
+            <TextBlock x:Name="VersionText"
+                       FontSize="11"
+                       Foreground="#B9C0CC"
+                       Text="0.0.0-dev (Administrate)" />
+          </Border>
+
+          <TextBlock x:Name="StatusText"
+                     Grid.Column="1"
+                     FontSize="11"
+                     Foreground="#B9C0CC"
+                     HorizontalAlignment="Right"
+                     Text="Initializing..." />
+        </Grid>
+
+        <ProgressBar x:Name="ProgressIndicator"
+                     Grid.Row="1"
+                     Minimum="0"
+                     Maximum="100"
+                     Value="0"
+                     Height="4"
+                     IsIndeterminate="False"
+                     Foreground="#F6F7FB"
+                     Background="#2C313D" />
+      </Grid>
+    </Border>
   </Grid>
 </Window>