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/lib/api.ts

@@ -1075,6 +1075,9 @@ export const api = {
     req(`/api/downloads/${id}/storyboard`),
   downloads: (): Promise<DownloadJob[]> => req("/api/downloads"),
   downloadsShared: (): Promise<DownloadJob[]> => req("/api/downloads/shared"),
+  // Remove a shared-with-me item from your list (deletes only your share grant, not the file).
+  removeSharedDownload: (jobId: number): Promise<{ removed: number }> =>
+    req(`/api/downloads/shared/${jobId}`, { method: "DELETE" }),
   downloadUsage: (): Promise<DownloadUsage> => req("/api/downloads/usage"),
   downloadIndex: (): Promise<Record<string, DownloadStatus>> => req("/api/downloads/index"),
   pauseDownload: (id: number): Promise<DownloadJob> =>