feat: implement video job management with retry and delete functionality, enhance video generation status tracking

Co-authored-by: Copilot <copilot@github.com>

backend/app/routers/admin.py

@@ -185,3 +185,43 @@ async def admin_mark_timed_out(_: dict = Depends(require_admin)) -> dict[str, in
     conn = get_conn()
     count = mark_timed_out_video_jobs(conn, timeout_minutes=120)
     return {"timed_out": count}
+
+
+@router.post("/videos/{job_id}/retry", status_code=200)
+async def admin_retry_video_job(job_id: str, _: dict = Depends(require_admin)) -> dict[str, str]:
+    """Reset a failed or cancelled video job back to 'queued' for reprocessing."""
+    conn = get_conn()
+    lock = get_write_lock()
+    now = datetime.now(timezone.utc)
+    async with lock:
+        row = conn.execute(
+            "SELECT status FROM generated_videos WHERE id = ?", [job_id]
+        ).fetchone()
+        if row is None:
+            from fastapi import HTTPException
+            raise HTTPException(status_code=404, detail="Job not found")
+        if row[0] not in ("failed", "cancelled"):
+            from fastapi import HTTPException
+            raise HTTPException(
+                status_code=400, detail=f"Cannot retry job with status '{row[0]}'")
+        conn.execute(
+            "UPDATE generated_videos SET status = 'queued', updated_at = ? WHERE id = ?",
+            [now, job_id],
+        )
+    return {"status": "ok", "job_id": job_id}
+
+
+@router.delete("/videos/{job_id}", status_code=200)
+async def admin_delete_video_job(job_id: str, _: dict = Depends(require_admin)) -> dict[str, str]:
+    """Permanently delete a video job record."""
+    conn = get_conn()
+    lock = get_write_lock()
+    async with lock:
+        row = conn.execute(
+            "SELECT id FROM generated_videos WHERE id = ?", [job_id]
+        ).fetchone()
+        if row is None:
+            from fastapi import HTTPException
+            raise HTTPException(status_code=404, detail="Job not found")
+        conn.execute("DELETE FROM generated_videos WHERE id = ?", [job_id])
+    return {"status": "ok", "job_id": job_id}