feat(design): the download, notification and Scheduler action lists (C1) — the rows' "…", the band's and the strip's "…" (E28 S3e3)

A download row keeps play (pause / resume / retry in the queue) and the save link; the editors,
sharing, re-download, the copies and cancel / delete / remove moved into its "…"
(useDownloadActions). A link inside the row keeps the browser's own right-click menu. A
notification row keeps its link and its unread mark and shows its dismiss on hover; an activity
notice's Find in feed and Undo are in its "…". The inbox band keeps Mark all read and puts Clear
everything, now behind a confirm, in its "…". The Scheduler strip keeps Run all and Pause and puts
Purge discovery in its "…". Polled lists key their menus by id (keyOf). ui/menuGroups draws a
rule only between two non-empty groups. Find in feed also drops the tag, search and age filters
that could hide the video it looks for.

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

@@ -1,5 +1,6 @@
 {
   "title": "Háttér-ütemező",
+  "menu": "Ütemező műveletei",
   "loading": "Ütemező betöltése…",
   "running": "Fut",
   "paused": "Szüneteltetve",