fix: require Python >=3.11 and lock scikit-learn deps for uv

scikit-learn 1.9.0 supports only Python >=3.11, so uv could not resolve
the >=3.9 range. The deployment runs 3.11. Also pins numpy back to
1.26.4 in the lockfile (pandas 2.0.3 ABI).

pyproject.toml

@@ -28,15 +28,13 @@ classifiers = [
     "Topic :: Scientific/Engineering :: Hydrology",
     "Topic :: System :: Monitoring",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.9",
-    "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
     "Operating System :: OS Independent",
     "Environment :: Web Environment",
     "Framework :: FastAPI"
 ]
-requires-python = ">=3.9"
+requires-python = ">=3.11"
 dependencies = [
     # Core dependencies
     "requests==2.31.0",