fix(diagnostics): say which read failed, and let Live restart

- "Load older" is not offered off a loading filter's placeholder rows,
  whose cursor belongs to the previous filter.
- A failed older page, stale rows and missing counts each get their own
  message (HU/EN).
- Live shows as off once a failed read stopped the polling; pressing it
  again reads now.

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

@@ -27,6 +27,8 @@
   "showJob": "Only this job's lines",
   "empty": "No lines match the filters.",
   "stale": "The last refresh failed; what you see may be out of date.",
+  "olderFailed": "Couldn't load the older lines.",
+  "countsFailed": "The filter counts didn't load.",
   "count_one": "{{count}} line loaded · newest first",
   "count_other": "{{count}} lines loaded · newest first",
   "older": "Load older",

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

@@ -27,6 +27,8 @@
   "showJob": "Csak ennek a jobnak a sorai",
   "empty": "Nincs a szűrésnek megfelelő sor.",
   "stale": "Az utolsó frissítés nem sikerült, amit látsz, elavult lehet.",
+  "olderFailed": "Nem sikerült betölteni a régebbi sorokat.",
+  "countsFailed": "A szűrők számai nem töltődtek be.",
   "count_one": "{{count}} sor betöltve · a legújabb felül",
   "count_other": "{{count}} sor betöltve · a legújabb felül",
   "older": "Régebbiek betöltése",