Fix bug where navigating into an empty folder in the DirectoryPicker
would automatically revert to the previous folder. The useEffect that
auto-fetches on open was using the stale 'value' prop instead of
'browser.currentPath' after navigation.
Also adds a 'New folder' button to the DirectoryPicker toolbar so users
can create folders directly when setting up a project.
- DirectoryPicker.tsx: fix useEffect to use browser.currentPath || value
- DirectoryPicker.tsx: add create folder UI state and handlers
- DirectoryPicker.css: styles for create folder input and actions
- routes.ts: add POST /api/create-directory endpoint
- legacy.ts: add createDirectory API client
- DirectoryPicker.test.tsx: add tests for empty folder nav and create folder
d8e325b17e