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/components/Channels.tsx

@@ -15,7 +15,7 @@ import {
 } from "lucide-react";
 import { api, HttpError, type ManagedChannel, type Tag } from "../lib/api";
 import { useDismiss } from "../lib/useDismiss";
-import { formatEta, formatViews, relativeTime } from "../lib/format";
+import { formatEta, formatTotalHours, formatViews, relativeTime } from "../lib/format";
 import { notify } from "../lib/notifications";
 import Tooltip from "./Tooltip";
 import DataTable, { type Column } from "./DataTable";
@@ -28,13 +28,6 @@ export type ChannelsView = "subscribed" | "discovery";
 
 export type ChannelStatusFilter = "all" | "needs_full" | "fully_synced" | "hidden";
 
-// Compact total-duration label for a whole channel (hours-scale, so H:MM:SS would be huge).
-function fmtTotalDuration(sec: number): string {
-  if (!sec) return "—";
-  const h = Math.round(sec / 3600);
-  return h >= 1 ? `${h.toLocaleString()} h` : `${Math.max(1, Math.round(sec / 60))} m`;
-}
-
 const STATUS_FILTERS: { id: ChannelStatusFilter; labelKey: string }[] = [
   { id: "all", labelKey: "channels.filters.all" },
   { id: "needs_full", labelKey: "channels.filters.needsFull" },
@@ -287,7 +280,7 @@ export default function Channels({
       nowrap: true,
       sortable: true,
       sortValue: (c) => c.total_duration_seconds,
-      render: (c) => <span className="text-muted tabular-nums">{fmtTotalDuration(c.total_duration_seconds)}</span>,
+      render: (c) => <span className="text-muted tabular-nums">{formatTotalHours(c.total_duration_seconds)}</span>,
     },
     {
       key: "types",