fix: use hermes_yaml with yaml fallback; add model column to default config

PyYAML is no longer installed in the Hermes venv since recent updates —
/sl failed at runtime with ModuleNotFoundError: No module named 'yaml'.
Now uses the core hermes_yaml module, falling back to PyYAML when present.

.gitignore

@@ -0,0 +1,2 @@
+__pycache__/
+docs/.bak/