feat: 应用图标 + 浅色/深色主题 + 消息复制 + 详情可选中复制

实现 4 个用户需求:

1. 应用图标(Gotify Ducker 吉祥物)
   - Assets/gotify-mascot.png:用户提供的 PNG(196x196)
   - Assets/Build-Icon.ps1:用 System.Drawing 高质量缩放生成多分辨率 ICO(16/24/32/48/64/128/196),PNG 数据嵌入 ICO 容器(Win10+ 原生支持)
   - Assets/gotify-mascot.ico:7 个分辨率的 PNG-in-ICO,41KB
   - WindowsGotify.csproj 加 <ApplicationIcon> 让 EXE 资源带这个图标
   - csproj 加 <None Update=Assets\gotify-mascot.ico><CopyToOutputDirectory> 发布时一并拷
   - TrayIconService 加 LoadMascotIcon() 静态方法,优先从 EXE 同目录 Assets\ 下找,找不到回退到 SystemIcons.Application
   - Windows 通知中心的 toast 会自动用 ApplicationIcon(无需单独设)

2. 浅色/深色主题
   - AppConfig 新增 UiConfig { Theme: "Light"|"Dark"|"System" }
   - Themes/Light.xaml + Themes/Dark.xaml:两个 ResourceDictionary,定义 WindowBackground/CardBackground/CardAltBackground/BorderColor/PrimaryText/SecondaryText/MutedText/AccentBrush/SuccessDot/ErrorDot/PendingDot/PriorityUrgent/High/Normal/Low 等
   - Services/ThemeService.cs:静态类,Apply(name) 卸载旧主题字典 + 加载新主题字典到 Application.Resources.MergedDictionaries,Changed 事件,Toggle() 切换
   - MainWindow.xaml 所有颜色全部改用 {DynamicResource Xxx},主题切换时立刻刷新
   - PriorityToBrushConverter 改用 Application.Current.TryFindResource("PriorityXxx") 拿色,跟着主题走
   - 主窗右上角加 ☼/☾ 切换按钮,点一下切主题并自动写回 config.json

3. 消息正文复制按钮
   - 详情面板"消息正文"标签右侧加 [复制] 按钮
   - CopyMessageButton_Click:用 System.Windows.Clipboard.SetText 把全文(应用名/标题/时间/优先级/正文/URL)写进剪贴板
   - 按钮反馈:复制后短暂显示"已复制"1.5 秒再恢复
   - BuildFullMessageText 静态方法统一格式化

4. 详情面板可选中复制
   - DetailMessage 从 TextBlock 改成 TextBox(IsReadOnly=True, BorderThickness=0, Background=Transparent, IsReadOnlyCaretVisible=True)
   - DetailTitle / DetailUrl 也改成 TextBox IsReadOnly,用户能 Ctrl+A 全选、鼠标拉黑
   - DetailUrl 双击打开(之前是单击,TextBlock 没法选中;TextBox 单击会进入文字选择模式影响双击识别,所以改成双击)

WPF+WinForms 双开:Application/Brush/Color/Clipboard/Button 多个类型两个命名空间都有,ThemeService/ValueConverters/MainWindow.xaml.cs 都加 using alias 固定走 WPF 的;TrayIconService 加 using System.IO 补 Path/File。

实测:新进程跑起来后 ApplicationCache refreshed count=6(用户新建了一个 app),WebSocket connected,真实消息流处理正常(短信号码 19999999999/15889931832),通知弹出。

Themes/Dark.xaml

@@ -0,0 +1,25 @@
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+
+    <SolidColorBrush x:Key="WindowBackground"  Color="#1E1E1E"/>
+    <SolidColorBrush x:Key="CardBackground"    Color="#2D2D30"/>
+    <SolidColorBrush x:Key="CardAltBackground" Color="#252526"/>
+    <SolidColorBrush x:Key="BorderColor"       Color="#3F3F46"/>
+    <SolidColorBrush x:Key="PrimaryText"       Color="#F0F0F0"/>
+    <SolidColorBrush x:Key="SecondaryText"     Color="#C8C8C8"/>
+    <SolidColorBrush x:Key="MutedText"         Color="#8A8A8A"/>
+    <SolidColorBrush x:Key="SubtleText"        Color="#6A6A6A"/>
+    <SolidColorBrush x:Key="AccentBrush"       Color="#4CC2FF"/>
+    <SolidColorBrush x:Key="AccentText"        Color="#0E0E0E"/>
+    <SolidColorBrush x:Key="SuccessDot"        Color="#16C60C"/>
+    <SolidColorBrush x:Key="ErrorDot"          Color="#F48771"/>
+    <SolidColorBrush x:Key="PendingDot"        Color="#FFB900"/>
+    <SolidColorBrush x:Key="MutedDot"          Color="#8A8A8A"/>
+
+    <SolidColorBrush x:Key="PriorityUrgent"    Color="#F48771"/>
+    <SolidColorBrush x:Key="PriorityHigh"      Color="#FFB900"/>
+    <SolidColorBrush x:Key="PriorityNormal"    Color="#9CDCFE"/>
+    <SolidColorBrush x:Key="PriorityLow"       Color="#8A8A8A"/>
+
+    <SolidColorBrush x:Key="ListItemSelected"  Color="#094771"/>
+</ResourceDictionary>

Themes/Light.xaml

@@ -0,0 +1,27 @@
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+
+    <SolidColorBrush x:Key="WindowBackground"  Color="#FAFAFA"/>
+    <SolidColorBrush x:Key="CardBackground"    Color="White"/>
+    <SolidColorBrush x:Key="CardAltBackground" Color="#F5F5F5"/>
+    <SolidColorBrush x:Key="BorderColor"       Color="#E0E0E0"/>
+    <SolidColorBrush x:Key="PrimaryText"       Color="#222222"/>
+    <SolidColorBrush x:Key="SecondaryText"     Color="#666666"/>
+    <SolidColorBrush x:Key="MutedText"         Color="#888888"/>
+    <SolidColorBrush x:Key="SubtleText"        Color="#999999"/>
+    <SolidColorBrush x:Key="AccentBrush"       Color="#0078D4"/>
+    <SolidColorBrush x:Key="AccentText"        Color="White"/>
+    <SolidColorBrush x:Key="SuccessDot"        Color="#108116"/>
+    <SolidColorBrush x:Key="ErrorDot"          Color="#D13438"/>
+    <SolidColorBrush x:Key="PendingDot"        Color="#CA5010"/>
+    <SolidColorBrush x:Key="MutedDot"          Color="#888888"/>
+
+    <!-- 优先级徽章颜色(P0..P4=一般, P5..P7=重要, P8+=紧急) -->
+    <SolidColorBrush x:Key="PriorityUrgent"    Color="#D13438"/>
+    <SolidColorBrush x:Key="PriorityHigh"      Color="#CA5010"/>
+    <SolidColorBrush x:Key="PriorityNormal"    Color="#4A5568"/>
+    <SolidColorBrush x:Key="PriorityLow"       Color="#888888"/>
+
+    <!-- 选中行高亮(在 ListView 里) -->
+    <SolidColorBrush x:Key="ListItemSelected"  Color="#E5F1FB"/>
+</ResourceDictionary>