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').

backend/app/routes/downloads.py

@@ -258,8 +258,12 @@ def enqueue_download(
 def enqueue_edit(
     payload: dict, user: User = Depends(require_human), db: Session = Depends(get_db)
 ) -> dict:
-    """Queue a phase-2 editor derivative (trim/crop) of one of the user's finished downloads."""
-    source_job = _own_job(db, user, int(payload.get("source_job_id") or 0))
+    """Queue a phase-2 editor derivative (trim/crop) of a download this user can access.
+
+    The source may be the user's own download OR one shared with them — either way the resulting
+    clip is a NEW per-user derivative in the editor's own library (counts against their quota); the
+    source file is only read, never modified, so editing a shared video is safe."""
+    source_job = _accessible_job(db, user, int(payload.get("source_job_id") or 0))
     if source_job.status != "done" or source_job.asset_id is None:
         raise HTTPException(status_code=409, detail="You can only edit a finished download.")
     spec = payload.get("edit_spec")
@@ -619,6 +623,24 @@ def unshare_download(
     return {"ok": True}
 
 
+@router.delete("/shared/{job_id}")
+def remove_shared_with_me(
+    job_id: int, user: User = Depends(require_human), db: Session = Depends(get_db)
+) -> dict:
+    """Remove a download that was shared WITH this user from their 'Shared with me' list. Deletes
+    only the recipient's share grant — the owner's job and the physical file are untouched (this is
+    a per-user dismissal, not a delete)."""
+    row = db.execute(
+        select(DownloadShare).where(
+            DownloadShare.job_id == job_id, DownloadShare.to_user_id == user.id
+        )
+    ).scalar_one_or_none()
+    if row is not None:
+        db.delete(row)
+        db.commit()
+    return {"removed": job_id}
+
+
 # --- recipients (for the internal "share with a user" picker) ------------------------------
 
 @router.get("/recipients")