SIENTIAPDE-1973: fix(deps): make the gateway requirements installable from the cluster index

Workers install only from the cluster package index (install-entrypoint.sh:
pip install --index-url $PYPI_SERVER). The 2.0.0-rc1 deploy never became Ready
because two new requirements are not mirrored there:

- grpcio-tools: only needed to regenerate ingestor/proto/*_pb2*.py, which are
  committed. Moved to requirements-dev.txt (nothing imports grpc_tools).
- nats-py: needed at runtime; mirrored by library-distribution-controller#92.

Also declares protobuf>=7.35 explicitly: the committed stubs were generated with
protobuf 7.35.0 and validate the runtime version on import; until now it only
arrived transitively. The mirror carries 7.36.x.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

requirements-dev.txt

@@ -16,4 +16,9 @@ pytest-asyncio>=0.21.0   # Async test support (already in main requirements)
 
 # Development Tools
 ipython>=8.12.0          # Enhanced Python shell
-ipdb>=0.13.13            # IPython debugger
+ipdb>=0.13.13            # IPython debugger
+
+# gRPC code generation (regenerate ingestor/proto/*_pb2*.py) — not needed
+# at runtime: the generated stubs are committed. Kept out of requirements.txt
+# because workers install only from the cluster package index.
+grpcio-tools>=1.60