feat(filesystem): add create-folder API for workspace picker

Adds a secure endpoint for creating a single subfolder in the current filesystem listing, and wires the non-native directory browser UI to create + enter the new folder.

packages/ui/src/styles/components/directory-browser.css

@@ -81,6 +81,14 @@
   width: auto;
 }
 
+.directory-browser-current-actions {
+  display: flex;
+  align-items: center;
+  gap: var(--space-sm);
+  flex-wrap: wrap;
+  justify-content: flex-end;
+}
+
 .directory-browser-close {
 
   display: inline-flex;