Remove 'spaces' from requirements: pre-installed by HF ZeroGPU runtime

Installing spaces from PyPI overwrites the pre-installed ZeroGPU version
and breaks the @spaces.GPU GPU proxy (RuntimeError: Found no NVIDIA driver).
HF pre-installs the correct ZeroGPU-aware version in the base image.
Also bump cache-bust to 7 to force fresh Docker layer.

requirements.txt

@@ -1,5 +1,5 @@
-# HuggingFace ZeroGPU Space — Gradio SDK  [cache-bust: 6]
-spaces
+# HuggingFace ZeroGPU Space — Gradio SDK  [cache-bust: 7]
+# spaces: pre-installed by HF ZeroGPU runtime; DO NOT reinstall from PyPI (breaks GPU proxy)
 numpy>=2
 
 # Git-pinned installs