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.

src/ClaudeDo.Localization/locales/en.json

@@ -407,7 +407,10 @@
       "body": "ClaudeDo can't reach the background worker. It is normally started automatically at logon. You can start it now, or reinstall if the problem persists.",
       "dismiss": "Dismiss",
       "rerunInstaller": "Rerun Installer",
-      "startWorker": "Start Worker"
+      "startWorker": "Start Worker",
+      "workerNotFound": "Worker executable not found. Check the installation.",
+      "installerNotFound": "Installer not found. Check the installation.",
+      "startFailed": "Start failed: {0}"
     },
     "listSettings": {
       "title": "LIST SETTINGS",
@@ -777,7 +780,7 @@
   },
   "vm": {
     "connection": { "online": "Online", "connecting": "Connecting…", "offline": "Offline" },
-    "shell": { "restartingWorker": "Restarting worker…", "unexpectedError": "Unexpected error: {0}" },
+    "shell": { "unexpectedError": "Unexpected error: {0}" },
     "mainWindow": { "closeConfirm": { "message": "{0} Mission Control session(s) are still running. Closing the app will end them. Close anyway?" } },
     "agentStatus": { "idle": "Idle", "queued": "Queued", "running": "Running", "review": "Review", "children": "Waiting for Subtasks", "done": "Done", "failed": "Failed", "cancelled": "Cancelled" },
     "taskStatus": { "idle": "Idle", "queued": "Queued", "running": "Running", "waitingForReview": "Waiting for Review", "waitingForChildren": "Waiting for Subtasks", "done": "Done", "failed": "Failed", "cancelled": "Cancelled", "parked": "Parked", "interactive": "Interactive", "waiting": "Waiting" },