fix: add plotly to requirements.txt to resolve HF Space runtime error

requirements.txt

@@ -81,6 +81,8 @@ markupsafe==3.0.3
     #   jinja2
 mdurl==0.1.2
     # via markdown-it-py
+narwhals==2.19.0
+    # via plotly
 networkx==3.6.1
     # via stl-to-gcode
 numpy==2.4.4
@@ -98,12 +100,15 @@ packaging==26.0
     #   gradio
     #   gradio-client
     #   huggingface-hub
+    #   plotly
 pandas==3.0.1
     # via gradio
 pillow==12.1.1
     # via
     #   gradio
     #   stl-to-gcode
+plotly==6.7.0
+    # via stl-to-gcode
 pydantic==2.12.5
     # via
     #   fastapi