Fix #32: revert gradio pin to unblock HF build (#33)

HF Spaces' build wrapper appends gradio==<sdk_version> (currently 6.5.1
per README.md) to the pip install command. The gradio>=5,<6 pin from #30
collides with that, causing ResolutionImpossible at HF build time.

The actual runtime fix from #30 is the ssr_mode=False argument to
demo.launch, which is left unchanged. The requirements.txt pin was a
defensive belt-and-braces that conflicts with HF's own pin and should
not have been added.

requirements.txt

@@ -5,7 +5,7 @@ numpy
 pybioclip
 faiss-cpu
 duckdb
-gradio>=5,<6
+gradio
 Pillow
 requests
 huggingface_hub