📝 align runtime file examples

docs/api/file-sink-policy.md

@@ -55,7 +55,7 @@ In this example, the file policy can be passed around as one typed value instead
 
 When current file behavior should be read, adjusted, and written back:
 ```moonbit
-let policy = sink.file_policy()
+let policy = runtime.file_policy()
 let next = FileSinkPolicy::new(
   append=policy.append,
   auto_flush=false,

docs/api/file-sink-state.md

@@ -52,7 +52,7 @@ In this example, availability, policy, and failure counters are captured togethe
 
 When a snapshot should be serialized for logs or support output:
 ```moonbit
-println(stringify_file_sink_state(logger.file_state(), pretty=true))
+println(stringify_file_sink_state(runtime.file_state(), pretty=true))
 ```
 
 In this example, the typed snapshot becomes readable JSON without manual field assembly.