fix(installer): reject CurrentUser service account without password

src/ClaudeDo.Installer/Steps/RegisterServiceStep.cs

@@ -46,10 +46,9 @@ public sealed class RegisterServiceStep : IInstallStep
         var createArgs = $"create {ServiceName} binPath= \"{workerExe}\" start= {startType}";
 
         if (ctx.ServiceAccount == "CurrentUser")
-        {
-            var username = Environment.UserName;
-            createArgs += $" obj= \".\\{username}\"";
-        }
+            return StepResult.Fail(
+                "Service cannot run as Current User without a password. " +
+                "Select 'Local System' or extend ServicePage to capture a password.");
 
         progress.Report("Creating service...");
         var (exitCode, output) = await RunSc(createArgs, ctx, progress, ct);