fix(hf-space): bump Gradio to 5.x to fix HfFolder ImportError

Build on AshwinP/compounding-test failed at startup with:

ImportError: cannot import name 'HfFolder' from 'huggingface_hub'

Cause: Gradio 4.x imports the now-removed HfFolder symbol from
huggingface_hub in its oauth.py. huggingface_hub>=1.0 (pulled in by
our `huggingface_hub>=0.27` floor and pip resolving to latest) removed
HfFolder. Gradio 5.0 (Oct 2024) dropped the HfFolder dependency and
uses HfApi/get_token instead.

Fix:
requirements.txt gradio>=4.0 → gradio>=5.0 (with a comment
explaining why the floor matters)
README.md sdk_version: 4.44.0 → 5.9.1

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -4,7 +4,7 @@ emoji: 📈
 colorFrom: indigo
 colorTo: purple
 sdk: gradio
-sdk_version: 4.44.0
+sdk_version: 5.9.1
 app_file: app.py
 pinned: false
 license: mit

requirements.txt

@@ -1,5 +1,8 @@
 # Core (always required)
-gradio>=4.0
+# Gradio 5.x is required — earlier 4.x versions import the now-removed
+# `HfFolder` symbol from `huggingface_hub`, breaking the Space at startup
+# when paired with huggingface_hub>=1.0.
+gradio>=5.0
 python-dotenv>=1.0
 pytest>=8.0