feat(plugins): let window commands choose folders and open projects (#1998)

Adds API 1.3 `ui.pick-directory` (native folder chooser, same window/budget rules as `pick`) and `workspace.open-project(path, new-window)`, which goes through the normal File › Open flow with its trust prompt, window reuse and unsaved-change handling. Paths are absolute on the UI machine and validated by the host whatever its OS. Closes #1959.

Co-authored-by: arnaud-ritti <[email protected]>

plugins/official/string-tools/dist/plugin.wasm.sources

@@ -1 +1 @@
-73b65742330387b7dbf498c6ec275ab41a55475243d771c1274de70b939c327f
+82547cce827ac884aafed961134e5d54be3dcd937990a3c372dfcdd8102aea23