feat(workspace): find projects under a chosen folder (#2167)

Adding projects to a workspace took one folder at a time. Choosing a folder that is not itself a project now scans below it, up to four levels and a shared entry budget, without following symlinks or descending into a project and skipping dependency, output and hidden directories. The projects found appear in a checklist with linked ones disabled; a folder with none is added as before. The scan is cancellable and runs in both the create and manage dialogs.

Fixes #2102

src/features/app/WorkspaceDialog.module.css

@@ -66,3 +66,9 @@
 .error {
   color: var(--danger);
 }
+.candidate {
+  display: flex;
+  flex-direction: column;
+  gap: 3px;
+  overflow-wrap: anywhere;
+}