Pin deps and let the Space own gradio

requirements.txt

@@ -1,3 +1,6 @@
-gradio
-fastmcp>=4.0
-pydantic>=2.0
+# gradio is installed by the Space itself from sdk_version in README.md.
+# Listing it unpinned here made pip resolve it against the Space's own
+# gradio[oauth,mcp]==6.31.0 and the solve ran away: "resolution-too-deep".
+# Pin what we actually need and let the Space own its SDK.
+fastmcp==4.1.6
+pydantic>=2.9,<3