feat(downloads): edit + remove actions on shared-with-me items (no re-share)

A shared-with-me item only had a download button. Add two actions (Share is intentionally NOT
offered — no chain re-sharing of someone else's file):
- Edit: the editor now accepts an accessible (owned OR shared) source, so editing a shared video
  produces the editor's OWN clip in their library (counts against their quota, fully theirs
  including share); the source file is only read. Route uses _accessible_job.
- Remove from my list: DELETE /api/downloads/shared/{job_id} deletes only the recipient's share
  grant — the owner's job and physical file are untouched (per-user dismissal).
i18n en/hu/de. Verified in a real browser (edit a shared 70-min video → own 2:31 clip; remove
confirm shows 'won't delete the owner's file').

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

@@ -57,7 +57,8 @@
     "download": "Save to my device",
     "rename": "Rename",
     "share": "Share",
-    "edit": "Edit / trim"
+    "edit": "Edit / trim",
+    "removeShared": "Remove from my list"
   },
   "empty": {
     "queue": "Nothing in the queue.",
@@ -110,7 +111,9 @@
     "cancelTitle": "Cancel download?",
     "cancelBody": "This stops the download and removes it from your queue.",
     "deleteTitle": "Remove download?",
-    "deleteBody": "This removes it from your list. The file may stay cached for other users until it expires."
+    "deleteBody": "This removes it from your list. The file may stay cached for other users until it expires.",
+    "removeSharedTitle": "Remove from your list?",
+    "removeSharedBody": "This removes it from your shared list only — it won't delete the owner's file."
   },
   "profiles": {
     "manage": "Manage formats",