Render folder studio progressively

[cbusillo]

Summary

• make the nested folder-studio route return route identity synchronously instead of blocking SvelteKit load on folder/status/host APIs
• hydrate folder studio data client-side with typed placeholder payloads, stale-response guards, and same-route prefix refresh
• keep the Folder Studio shell mounted during slow or failed API calls, with loading workflow copy and no enabled mutation buttons until real data arrives
• replace invalidateAll()-dependent post-action refresh with an explicit onMutate refresh callback now that route load no longer fetches folder data

Validation

• bash scripts/pre-commit-check.sh
• Browser direct-opened a real /folders/<prefix> URL at http://127.0.0.1:4173 and verified the real Folder Studio surface renders
• Playwright delayed /api/folders/... responses: before API release, .operator-shell, title, crumb, and Loading folder state were visible, with no enabled live mutation buttons; after release, the real workflow hydrated in place
• Playwright mobile viewport 390x844: no horizontal overflow on the folder-studio route

Notes

• This finishes the old route-loading-wall pattern for the nested folder studio path that remained after the top-level progressive rendering pass.