implement review feedback, add auth, logging, and improve robustness

servers/slack/requirements.txt

@@ -1,6 +1,8 @@
-fastapi
-uvicorn[standard]
-pydantic
-python-multipart
-httpx
-python-dotenv
+fastapi>=0.110.0,<0.111.0
+uvicorn[standard]>=0.29.0,<0.30.0
+pydantic>=2.6.0,<3.0.0
+httpx>=0.27.0,<0.28.0
+python-dotenv>=1.0.0,<2.0.0
+# NOTE: Run 'pip freeze > requirements.txt' in a virtual environment
+#       to capture the exact versions of all transitive dependencies
+#       for truly reproducible builds.