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/components/DownloadCenter.tsx

@@ -428,6 +428,12 @@ export default function DownloadCenter({ me }: { me: Me }) {
     onSuccess: invalidate,
   });
 
+  // Remove a shared-with-me item from your list (only your grant; the owner's file is untouched).
+  const removeShared = useMutation({
+    mutationFn: (id: number) => api.removeSharedDownload(id),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["downloads-shared"] }),
+  });
+
   const confirmThen = async (title: string, body: string, fn: () => void) => {
     if (await confirm({ title, message: body, confirmLabel: title, danger: true })) fn();
   };
@@ -545,6 +551,24 @@ export default function DownloadCenter({ me }: { me: Me }) {
           {(sharedQ.data ?? []).map((job) => (
             <DownloadRow key={job.id} job={job}>
               {job.can_download && saveBtn(job)}
+              {job.can_download && (job.asset?.duration_s ?? 0) > 0 && (
+                <IconBtn onClick={() => setEditJob(job)} title={t("downloads.actions.edit")}>
+                  <Scissors className="w-4 h-4" />
+                </IconBtn>
+              )}
+              <IconBtn
+                onClick={() =>
+                  confirmThen(
+                    t("downloads.confirm.removeSharedTitle"),
+                    t("downloads.confirm.removeSharedBody"),
+                    () => removeShared.mutate(job.id)
+                  )
+                }
+                title={t("downloads.actions.removeShared")}
+                danger
+              >
+                <Trash2 className="w-4 h-4" />
+              </IconBtn>
             </DownloadRow>
           ))}
           {sharedQ.data && sharedQ.data.length === 0 && (