feat: add configurable tool call blocking and monitoring

internal/handler/config_file.go

@@ -0,0 +1,8 @@
+package handler
+
+import "sync"
+
+// configFileMu serializes complete read-modify-write transactions across
+// handlers that share config.yaml. Per-handler locks cannot prevent lost
+// updates when another settings page saves a different YAML section.
+var configFileMu sync.Mutex