With a document open in the web app, Place Embedded was disabled because its menu enablement inherited the engine's native-filesystem check, although the menu path reads the picker's bytes and never touches a path. Place Embedded is now enabled whenever a document and a file-dialog service exist; Place Linked keeps the engine's native guard, since the web could only link to a bare file name (caught in #5817 by Higgs32584). An enablement test runs with the native check forced off, and a file-dialog test covers the browser answer shape, cancel, invalid bytes and the Free Transform handoff.
Fixes#1209. Fixes#5749.