feat(installer): add WPF installer/configurator project

Standalone WPF app (ClaudeDo.Installer) that handles full installation
and ongoing configuration of ClaudeDo. Two modes: wizard for first run,
tabbed settings panel for subsequent launches. Page-based extensibility
via IInstallerPage interface — adding new config sections requires only
one new class.

Install pipeline: dotnet publish, deploy binaries, write configs, init
DB (via SchemaInitializer from ClaudeDo.Data), register Windows Service,
create shortcuts. Dark theme matching the Avalonia app (forest teal accent).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Installer/Core/DarkTitleBar.cs

@@ -0,0 +1,29 @@
+using System.Runtime.InteropServices;
+using System.Windows;
+using System.Windows.Interop;
+
+namespace ClaudeDo.Installer.Core;
+
+public static class DarkTitleBar
+{
+    [DllImport("dwmapi.dll", PreserveSig = true)]
+    private static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int attrValue, int attrSize);
+
+    private const int DWMWA_USE_IMMERSIVE_DARK_MODE = 20;
+
+    public static void Apply(Window window)
+    {
+        if (window.IsLoaded)
+            SetDarkMode(window);
+        else
+            window.SourceInitialized += (_, _) => SetDarkMode(window);
+    }
+
+    private static void SetDarkMode(Window window)
+    {
+        var hwnd = new WindowInteropHelper(window).Handle;
+        if (hwnd == IntPtr.Zero) return;
+        int value = 1;
+        DwmSetWindowAttribute(hwnd, DWMWA_USE_IMMERSIVE_DARK_MODE, ref value, sizeof(int));
+    }
+}