Platform.SIGNAL was missing from default_toolset_map and platform_config_key
in gateway/run.py, causing Signal to silently fall back to hermes-telegram
toolset (same bug as HomeAssistant, fixed in PR #538).
Also updates:
- tests/test_toolsets.py: include hermes-signal and hermes-homeassistant in
the platform core-tools consistency check
- cli-config.yaml.example: document signal and homeassistant platform keys