feat(installer): add Diagnose section to SettingsWindow

Re-runs the environment checks against the installed configuration
(worker.config.json + detected install dir) without blocking navigation
and without auto-running on window open, only on a "Recheck" click.

Extracted the check-row rendering and check-run logic (busy state,
summary, Recheck command) out of SystemCheckPage into a shared
Checks/CheckListViewModel + Checks/CheckListView, composed by both
SystemCheckPage (wizard) and the new DiagnosePage (settings) instead
of duplicating it.

src/ClaudeDo.Localization/locales/de.json

@@ -531,6 +531,10 @@
       "subtitle": "Klicke auf Installieren, um ClaudeDo zu erstellen und bereitzustellen.",
       "launch": "ClaudeDo starten"
     },
+    "diagnose": {
+      "title": "Diagnose",
+      "subtitle": "Führt die Systemprüfungen erneut aus, gegen deine installierte Konfiguration."
+    },
     "settings": {
       "removeUserData": "Benutzerdaten entfernen (Aufgaben, Logs, Konfigurationen in ~/.todo-app)",
       "uninstall": "Deinstallieren",