packaging/web: say that ?host=parent takes precedence over data-host="page"

packaging/web/README.md

@@ -123,8 +123,10 @@ await init({ module_or_path: "./pdfcraft-web-<hash>_bg.wasm" });
 - Saves are not downloads in this mode: the `bytes` in `pdfcraft:save` hold the saved PDF, and
   the host decides where the file goes.
 - `?author=<name>` still signs the user's comments, as with `?host=parent`.
-- An unframed page that uses `?host=parent` keeps the normal app with downloads; only
-  `data-host="page"` turns this mode on.
+- An unframed page that uses `?host=parent` keeps the normal app with downloads.
+  `data-host="page"` turns this mode on only when `?host=parent` is absent: if `?host=parent` is
+  present it takes precedence, so a same-origin framed page uses the parent bridge, while an
+  unframed or cross-origin page gets no bridge and keeps normal downloads.
 
 ## Renderer selection and fallback flags