feat(downloads): editor UI — trim/split/crop clips (phase 2)

VideoEditor modal on a finished Library download: HTML5 <video> scrubber, filmstrip timeline
(lazy server storyboard sprite) with draggable in/out handles, draggable/resizable crop overlay,
per-edit Precise (re-encode) vs Fast (stream-copy) cut toggle, split-into-N fan-out (N trim jobs),
optional clip name. Edited clips show a 'Clip' badge; 'editing' phase gets a % bar. New api
enqueueEdit/downloadStoryboard/storyboardImageUrl + EditSpec type; editor i18n (en/hu/de).

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

@@ -45,7 +45,8 @@
     "thumbnail": "Vorschaubild einbetten",
     "sponsorblock": "Sponsoren entfernen",
     "metadata": "Metadaten schreiben",
-    "processing": "Verarbeitung"
+    "processing": "Verarbeitung",
+    "editing": "Bearbeitung"
   },
   "actions": {
     "pause": "Pause",
@@ -55,7 +56,8 @@
     "retry": "Erneut",
     "download": "Auf mein Gerät speichern",
     "rename": "Umbenennen",
-    "share": "Teilen"
+    "share": "Teilen",
+    "edit": "Bearbeiten / schneiden"
   },
   "empty": {
     "queue": "Die Warteschlange ist leer.",
@@ -142,5 +144,6 @@
     "status": "Status",
     "added": "Hinzugefügt",
     "user": "Nutzer"
-  }
+  },
+  "clipBadge": "Clip"
 }