Fixes #30230.

Summary:

• Add launchd SoftResourceLimits and HardResourceLimits for NumberOfFiles=4096 to the generated gateway plist.
• Keep the current main-branch KeepAlive shape while adding the fd limits.
• Add a regression test so macOS user-agent installs keep the higher fd limit.

Verification:

• python -m pytest tests/hermes_cli/test_gateway_service.py::TestProfileArg::test_launchd_plist_raises_file_descriptor_limit -q was the original red test on macOS before the plist change.
• .venv\\Scripts\\python.exe -m pytest tests/hermes_cli/test_gateway_service.py::TestProfileArg::test_launchd_plist_raises_file_descriptor_limit -q --timeout-method=thread -> skipped on Windows because the module imports POSIX pwd/grp.
• .venv\\Scripts\\python.exe -m pytest tests/hermes_cli/test_gateway_service.py -q -k "launchd or ProfileArg" --timeout-method=thread -> skipped on Windows for the same module-level POSIX import.
• Direct Windows smoke of generate_launchd_plist() -> confirmed SoftResourceLimits, HardResourceLimits, two NumberOfFiles keys, and <integer>4096</integer>.
• .venv\\Scripts\\python.exe -m ruff check hermes_cli/gateway.py tests/hermes_cli/test_gateway_service.py -> passed.
• git diff --check -> passed.

Note: full tests/hermes_cli/test_gateway_service.py still needs a POSIX/macOS host to execute rather than skip.