refactor: drop the remaining single-implementation interfaces

IBaseDirtyChecker, IInteractiveLaunchSpecService and the LaunchSpec wrapper
had one implementation and one caller each; ProcessRunnerAdapter existed only
to give a static class an interface, and InstallArtifactLocator used
inheritance for two constructor arguments. The external MCP container now
shares its singletons through a Share<T> helper instead of 17 near-identical
registrations.

src/ClaudeDo.Installer/App.xaml.cs

@@ -128,7 +128,7 @@ public partial class App : Application
 
         // Environment checks — stateless, so their infrastructure is shared; ClaudeCliLookup is
         // rebuilt per EnvironmentCheckService instance so a re-check doesn't reuse a stale result.
-        sc.AddSingleton<IProcessRunner, ProcessRunnerAdapter>();
+        sc.AddSingleton<IProcessRunner, ProcessRunner>();
         sc.AddSingleton<IProcessLauncher, ProcessLauncher>();
         sc.AddSingleton<IPortOwnerResolver, NetstatPortOwnerResolver>();
         sc.AddSingleton<ClaudeHelpLauncher>();

src/ClaudeDo.Installer/Core/ProcessRunner.cs

@@ -2,10 +2,17 @@ using System.Diagnostics;
 using System.IO;
 using System.Text;
 
+using ClaudeDo.Installer.Core.Interfaces;
+
 namespace ClaudeDo.Installer.Core;
 
-public static class ProcessRunner
+public sealed class ProcessRunner : IProcessRunner
 {
+    /// The injectable, progress-less shape. Everything else calls the static overload directly.
+    public Task<(int ExitCode, string Output)> RunAsync(
+        string fileName, string arguments, string? workingDirectory, CancellationToken ct)
+        => RunAsync(fileName, arguments, workingDirectory, progress: null, ct);
+
     public static async Task<(int ExitCode, string Output)> RunAsync(
         string fileName,
         string arguments,

src/ClaudeDo.Installer/Core/ProcessRunnerAdapter.cs

@@ -1,9 +0,0 @@
-using ClaudeDo.Installer.Core.Interfaces;
-
-namespace ClaudeDo.Installer.Core;
-
-public sealed class ProcessRunnerAdapter : IProcessRunner
-{
-    public Task<(int ExitCode, string Output)> RunAsync(string fileName, string arguments, string? workingDirectory, CancellationToken ct) =>
-        ProcessRunner.RunAsync(fileName, arguments, workingDirectory, progress: null, ct);
-}