fix(ui): surface worker connect/restart failures instead of no-opting

WorkerConnectionModalViewModel's StartWorker/RerunInstaller swallowed
missing-exe and Process.Start failures behind an empty catch and closed
the dialog anyway, looking like success. Now both show an inline error
and keep the dialog open; only a real launch closes it.

IslandsShellViewModel.RestartWorkerAsync never checked whether the
relaunched worker actually stayed up, and its status property was never
bound in any view. RestartWorkerService now fails if the new process
exits within a short survival window, and the outcome routes through
the footer error/success strip instead of the dead RestartWorkerStatus.

InstallArtifactLocator.Find() is now virtual and its two subclasses
unsealed so tests can fake exe resolution without touching the real
filesystem/registry.

tests/ClaudeDo.Ui.Tests/IslandsShellViewModelRestartWorkerTests.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Threading.Tasks;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Ui.ViewModels;
+
+namespace ClaudeDo.Ui.Tests;
+
+// Covers the "restart worker" footer feedback fix: RestartWorkerStatus used to be set but was
+// never bound in any view, so a died-on-launch worker (e.g. a port conflict, see #292) restarted
+// silently. RestartWorkerOperation is a test seam standing in for the real kill-and-relaunch +
+// short-timeout survival check, so these tests only assert the success/failure routing to the
+// shared footer strip (WorkerLogText/WorkerLogLevel), not real process spawning.
+public class IslandsShellViewModelRestartWorkerTests
+{
+    [Fact]
+    public async Task ProcessSurvives_FlashesFooterSuccess()
+    {
+        var vm = new IslandsShellViewModel { RestartWorkerOperation = () => Task.CompletedTask };
+
+        await vm.RestartWorkerCommand.ExecuteAsync(null);
+
+        Assert.Equal(WorkerLogLevel.Success, vm.WorkerLogLevel);
+        Assert.Contains("restarted", vm.WorkerLogText);
+        Assert.True(vm.IsWorkerLogVisible);
+    }
+
+    [Fact]
+    public async Task ProcessDiesWithinTimeout_FlashesFooterError()
+    {
+        var vm = new IslandsShellViewModel
+        {
+            RestartWorkerOperation = () => throw new InvalidOperationException("worker process exited immediately (code 1)")
+        };
+
+        await vm.RestartWorkerCommand.ExecuteAsync(null);
+
+        Assert.Equal(WorkerLogLevel.Error, vm.WorkerLogLevel);
+        Assert.Contains("worker process exited immediately", vm.WorkerLogText);
+        Assert.True(vm.IsWorkerLogVisible);
+    }
+}