Harden server draft sync (Save & Exit + post-login transfer)

messages/en/create/draftHydration.json

@@ -0,0 +1,4 @@
+{
+  "loadingSavedProgress": "Loading your saved progress…",
+  "conflictPrompt": "You have progress saved in this browser and a draft on your account.\n\nOK — load the account draft (discard the browser copy).\nCancel — keep this browser copy."
+}