📝 clarify library logger warn helper routing

docs/api/library-logger-warn.md

@@ -41,7 +41,7 @@ Detailed rules explaining key parameters and behaviors
 
 - This helper delegates to `warn(...)` on the wrapped logger, which in turn uses `log(Level::Warn, ...)`.
 - Warning records are useful for abnormal but non-fatal conditions.
-- Per-call target override is not exposed here; use `log(...)` when that is required.
+- This helper does not accept a per-call target override. It uses the facade's stored target unless the facade was derived earlier with `with_target(...)` or `child(...)`.
 - All sink-side wrappers still participate normally in the write path.
 - Broader composition helpers remain on the underlying `Logger[S]` and require `to_logger()` first.
 
@@ -69,6 +69,8 @@ In this example, the warning remains easy to filter and inspect later.
 
 And any shared context already carried by the facade still participates through the wrapped logger pipeline.
 
+And the write still uses the facade's stored target because this shortcut does not take a one-off `target=` override.
+
 ### Error Case
 
 e.g.: