fix(ui): gate Mission Control submit-for-review, add retry, fix event leak

Submit for Review is now disabled while a ConPTY pane is starting, has
failed to launch, or has already exited, and MissionControlViewModel
guards against a rapid double-click racing two SubmitTaskForReviewAsync
calls. A failed launch no longer permanently occupies its TaskId dedupe
slot -- a Retry button re-fetches the launch spec and restarts the pane
in place. CloseConPtySession/Dispose now also unsubscribe
SubmitForReviewRequested, matching the other pane event handlers. Also
fixes the pre-existing nullable-dereference warning in
IslandsShellViewModel.SyncInteractiveSessionChips.

src/ClaudeDo.Localization/locales/en.json

@@ -285,6 +285,8 @@
     "submitForReviewFailed": "Couldn't submit for review: {0}",
     "submitForReview": "Submit for review",
     "submitForReviewTip": "Commit this worktree and move the task to review so it can be merged",
+    "retry": "Retry",
+    "retryTip": "Try launching this session again",
     "planningTitleSuffix": " (Planning)",
     "question": {
       "title": "Claude is asking",