feat(config): expose enable_tool_security_policies as a feature flag (homeassistant-ai#966)

Wires the new addon-config toggle into FEATURE_FLAG_FIELDS so it appears
in the Server Settings tab and rides PR homeassistant-ai#1420's _save_feature_flags +
_supervisor_merge_and_post_options + _schedule_supervisor_self_restart
flow when toggled in addon mode.

Author: kingpanther13

src/ha_mcp/config.py

@@ -337,6 +337,7 @@ def validate_settings() -> tuple[bool, str | None]:
         "HAMCP_ENABLE_CUSTOM_COMPONENT_INTEGRATION",
         bool,
     ),
+    ("enable_tool_security_policies", "ENABLE_TOOL_SECURITY_POLICIES", bool),
 )
 
 # Override-file location is the same data dir that holds tool_config.json