Home tab: storage workspace refresh flicker, missing local previews, no Settings entry point

Three problems on the Home / new tab in 0.15.1.

• Storage workspace visibly re-renders on refresh and window focus. Every focus-triggered refresh flashes or empties the list before it repopulates. Keep the previous list rendered until new data arrives and update in place.
• Recent local files show no preview. .fig files recently opened from disk show a placeholder icon in Recent files instead of a thumbnail, while storage-backed documents do get one. Generate and cache a thumbnail for local files too.
• Settings is hard to reach. Settings lives at View › Preferences › Settings… (⌘,), which is not discoverable, and the only visible entry point on the Home tab is the "Configure storage before using this workspace" empty-state button, which disappears once storage is configured. Add a Settings entry on the Home tab and in the app menu, and surface the shortcut.