feat: enhance Home Assistant integration with service discovery and setup

Improvements to the HA integration merged from PR #184:

- Add ha_list_services tool: discovers available services (actions) per
  domain with descriptions and parameter fields. Tells the model what
  it can do with each device type (e.g. light.turn_on accepts brightness,
  color_name, transition). Closes the gap where the model had to guess
  available actions.

- Add HA to hermes tools config: users can enable/disable the homeassistant
  toolset and configure HASS_TOKEN + HASS_URL through 'hermes tools' setup
  flow instead of manually editing .env.

- Fix should-fix items from code review:
  - Remove sys.path.insert hack from gateway adapter
  - Replace all print() calls with proper logger (info/warning/error)
  - Move env var reads from import-time to handler-time via _get_config()
  - Add dedicated REST session reuse in gateway send()

- Update ha_call_service description to reference ha_list_services for
  action discovery.

- Update tests for new ha_list_services tool in toolset resolution.

toolsets.py

@@ -63,7 +63,7 @@ _HERMES_CORE_TOOLS = [
     # Honcho user context (gated on honcho being active via check_fn)
     "query_user_context",
     # Home Assistant smart home control (gated on HASS_TOKEN via check_fn)
-    "ha_list_entities", "ha_get_state", "ha_call_service",
+    "ha_list_entities", "ha_get_state", "ha_list_services", "ha_call_service",
 ]
 
 
@@ -198,7 +198,7 @@ TOOLSETS = {
 
     "homeassistant": {
         "description": "Home Assistant smart home control and monitoring",
-        "tools": ["ha_list_entities", "ha_get_state", "ha_call_service"],
+        "tools": ["ha_list_entities", "ha_get_state", "ha_list_services", "ha_call_service"],
         "includes": []
     },