fix: coerce show_reasoning and guard_agent_created config bools

Widens #16528 to two sibling sites that had the same quoted-boolean
bug: a YAML string "false" (or "0", "no", "off") silently evaluated
truthy under bool() / if-check.

- gateway/run.py _load_show_reasoning: is_truthy_value wrap
- tools/skill_manager_tool.py _guard_agent_created_enabled: is_truthy_value wrap
- regression tests for both

gateway/run.py

@@ -1742,7 +1742,10 @@ class GatewayRunner:
             if cfg_path.exists():
                 with open(cfg_path, encoding="utf-8") as _f:
                     cfg = _y.safe_load(_f) or {}
-                return bool(cfg_get(cfg, "display", "show_reasoning", default=False))
+                return is_truthy_value(
+                    cfg_get(cfg, "display", "show_reasoning"),
+                    default=False,
+                )
         except Exception:
             pass
         return False