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/Steps/WriteConfigStep.cs

@@ -0,0 +1,42 @@
+using ClaudeDo.Installer.Core;
+
+namespace ClaudeDo.Installer.Steps;
+
+public sealed class WriteConfigStep : IInstallStep
+{
+    public string Name => "Write Configuration";
+
+    public Task<StepResult> ExecuteAsync(InstallContext ctx, IProgress<string> progress, CancellationToken ct)
+    {
+        try
+        {
+            var workerCfg = new InstallerWorkerConfig
+            {
+                DbPath = ctx.DbPath,
+                SandboxRoot = ctx.SandboxRoot,
+                LogRoot = ctx.LogRoot,
+                WorktreeRootStrategy = ctx.WorktreeRootStrategy,
+                CentralWorktreeRoot = ctx.CentralWorktreeRoot,
+                QueueBackstopIntervalMs = ctx.QueueBackstopIntervalMs,
+                SignalRPort = ctx.SignalRPort,
+                ClaudeBin = ctx.ClaudeBin,
+            };
+            workerCfg.Save();
+            progress.Report("Written worker.config.json");
+
+            var uiCfg = new InstallerAppSettings
+            {
+                DbPath = ctx.UiDbPath,
+                SignalRUrl = ctx.SignalRUrl,
+            };
+            uiCfg.Save();
+            progress.Report("Written ui.config.json");
+
+            return Task.FromResult(StepResult.Ok());
+        }
+        catch (Exception ex)
+        {
+            return Task.FromResult(StepResult.Fail(ex.Message));
+        }
+    }
+}