fix: abort old loads, stale sync state, warn before unsaved edits are lost

public/i18n/en.json

@@ -205,6 +205,7 @@
     "SYNCING": "Syncing with Steam …",
     "SYNCING_FIRST_TIME": "First sync with Steam in progress. Your games will appear here shortly.",
     "SYNC_FAILED": "Sync failed. Please try again later.",
+    "SYNC_STALE": "The sync takes longer than usual. Reload the page later.",
     "LAST_SYNCED": "Last synced {{when}}",
     "FILTER_ALL": "All",
     "SEARCH_PLACEHOLDER": "Search games …",
@@ -705,5 +706,8 @@
     "RETRY": "Try again",
     "RETRY_FAILED": "Could not start the import again.",
     "ATTEMPT": "Try {{attempt}}: the last try made no progress."
+  },
+  "UNSAVED_CHANGES": {
+    "CONFIRM": "You have changes that are not saved. Leave this page and lose them?"
   }
 }