fix(review): resolve deep-review findings across quickfix batch #2

- Button: `loading` always disables (|| not ??) — stops a double-submit
  when a call-site passes an explicit boolean `disabled` (VideoEditor).
- playlists: track un-ingestable-but-live YouTube ids in the sync baseline
  so a linked playlist containing a private/deleted video converges instead
  of re-classifying it as a pending pull forever; re-attempt ingestion each
  sync so a restored (private->public) video heals, and prune ids that
  leave YouTube.
- SettingsPanel: download-auth section renders an honest error/loading
  state (StateMessage + retry) instead of a bare empty section on a failed
  credentials fetch; HU+EN loadError string.
- tests: reorder-order, partial-failure baseline hold, un-ingestable
  converge/heal/prune, Button loading-disables, download-auth error/retry.

frontend/src/i18n/locales/en/settings.json

@@ -122,7 +122,8 @@
     "failed": "Couldn't save those cookies.",
     "removeConfirmTitle": "Remove cookies?",
     "removeConfirmBody": "Downloads from this site will stop using your login.",
-    "removeConfirmAction": "Remove"
+    "removeConfirmAction": "Remove",
+    "loadError": "Couldn't load your download authentication settings."
   },
   "demo": {
     "title": "Demo access",

frontend/src/i18n/locales/hu/settings.json

@@ -122,7 +122,8 @@
     "failed": "A cookie-kat nem sikerült menteni.",
     "removeConfirmTitle": "Cookie-k eltávolítása?",
     "removeConfirmBody": "Az erről az oldalról induló letöltések nem használják tovább a bejelentkezésedet.",
-    "removeConfirmAction": "Eltávolítás"
+    "removeConfirmAction": "Eltávolítás",
+    "loadError": "Nem sikerült betölteni a letöltési hitelesítési beállításokat."
   },
   "demo": {
     "title": "Demo hozzáférés",