refactor(i18n,format): translate ETA strings; consolidate time/duration formatters

- formatEta was hardcoded English (violated the trilingual rule) -> time.eta.* keys
  in EN/HU/DE; Scheduler's countdown 'now' likewise.
- relativeFromMs added to format.ts; NotificationsPanel drops its duplicate
  relativeTime/relativeFromMs and the now-orphaned notifications.time.* keys.
- Channels' fmtTotalDuration moved to format.ts as formatTotalHours.

frontend/src/i18n/locales/de/notifications.json

@@ -11,11 +11,5 @@
   "openInManager": "Kanalverwaltung",
   "openOnYouTube": "Auf YouTube öffnen",
   "unhidden": "Eingeblendet „{{title}}”",
-  "unwatched": "Als nicht angesehen markiert „{{title}}”",
-  "time": {
-    "justNow": "gerade eben",
-    "minutes": "vor {{count}} Min.",
-    "hours": "vor {{count}} Std.",
-    "days": "vor {{count}} T."
-  }
+  "unwatched": "Als nicht angesehen markiert „{{title}}”"
 }

frontend/src/i18n/locales/de/time.json

@@ -6,5 +6,14 @@
   "daysAgo": "vor {{count}} T.",
   "weeksAgo": "vor {{count}} Wo.",
   "monthsAgo": "vor {{count}} Mon.",
-  "yearsAgo": "vor {{count}} J."
+  "yearsAgo": "vor {{count}} J.",
+  "eta": {
+    "now": "jetzt",
+    "done": "fertig",
+    "lessThanHour": "< 1 Stunde",
+    "hours_one": "~{{count}} Stunde",
+    "hours_other": "~{{count}} Stunden",
+    "days_one": "~{{count}} Tag",
+    "days_other": "~{{count}} Tage"
+  }
 }