fix(ui): review round 2 — reveal floor, failed next page, count states, row Play

- DataTable: the reveal floor holds only in the view it was made for (Channels
  never clears its follow, so every later sort mounted rows up to it)
- Feed + Plex browse: a failed next page stops the read-ahead and shows a row
  that retries, instead of re-requesting it once a round-trip
- the YouTube Load more click uses nextPageOnClick; a contract pins NEXT_PAGE
  to the read-aheads and the click sites to nextPageOnClick
- ItemCount: a failed count says so; a stale one says updating to a screen reader
- the narrow-picture Play lift applies only where a hover row is there to clear
- PlayerModal: one description ladder for the popover and the panel, both tested
- plexImage contract reads every img src, any attribute order
- Tabs comment names who persists the sub-tab

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

@@ -10,6 +10,9 @@
   "undo": "Undo",
   "redo": "Redo",
   "loading": "Loading…",
+  "loadMoreFailed": "Couldn't load more",
+  "countFailed": "Couldn't count the items",
+  "countUpdating": "updating",
   "somethingWrong": "Something went wrong",
   "itemCount_one": "{{formattedCount}} item",
   "itemCount_other": "{{formattedCount}} items",

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

@@ -10,6 +10,9 @@
   "undo": "Visszavonás",
   "redo": "Újra",
   "loading": "Betöltés…",
+  "loadMoreFailed": "Nem sikerült betölteni a továbbiakat",
+  "countFailed": "Nem sikerült megszámolni az elemeket",
+  "countUpdating": "frissül",
   "somethingWrong": "Hiba történt",
   "itemCount_one": "{{formattedCount}} elem",
   "itemCount_other": "{{formattedCount}} elem",