add UA headers to gif download

app.py

@@ -407,7 +407,7 @@ async def resolve_media_to_frames(media_input: str) -> List[Image.Image]:
     if media_input.startswith("http://") or media_input.startswith("https://"):
         hint = media_input
         session = await get_http_session()
-        async with session.get(media_input) as resp:
+        async with session.get(media_input, headers={"User-Agent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36", "Accept": "*/*"}) as resp:
             if resp.status != 200:
                 raise HTTPException(status_code=400, detail=f"download_failed: HTTP {resp.status}")
             # check content-length