fix(visualizer): improve dependency handling and multilingual JSON support

- Add Request to ImportError fallback block for dependency-free imports
- Replace Request hint to Request | None union type
- Add ensure_ascii=False to json.dumps() to preserve non-ASCII characters

Author: speedyk-005

src/chunklet/visualizer/visualizer.py

@@ -24,6 +24,7 @@
     File = lambda x: x  # noqa: E731
     Form = lambda x: x  # noqa: E731
     HTTPException = None
+    Request = None
     HTMLResponse = lambda x: x  # noqa: E731
     Response = lambda x: x  # noqa: E731
     StaticFiles = None
@@ -127,7 +128,7 @@ async def _chunk_file(
         file: UploadFile = File(...),
         mode: str = Form("document"),
         params: str = Form("{}"),
-        request: Request = None,
+        request: Request | None = None,
     ) -> Response:
         """Processes an uploaded file and returns chunked output.
 
@@ -196,7 +197,7 @@ async def _chunk_file(
                 )
 
             return Response(
-                content=json.dumps(response_data),
+                content=json.dumps(response_data, ensure_ascii=False),
                 media_type="application/json",
             )