Fixes#1243
Add sibling loading.tsx files for all 6 async route segments that were
missing instant loading UI, causing blank screens during navigation on
slow networks or cold caches.
Routes covered:
- /docs/[[...slug]] — awaits getDocPage + MDX body
- /blog — awaits source.getPages()
- /blog/[slug] — awaits params + MDX body
- /changelog — awaits source.getPages()
- /free — awaits getModels() fetch
- /free/[model_slug] — awaits Promise.all([getModel, getAllModels])
Each loading.tsx is a Server Component returning an animate-pulse
skeleton that matches its route's layout (header, content area,
grid/table/timeline as appropriate). Uses the Skeleton component and
Tailwind classes already present in the project.
Follows the pattern established in:
- app/dashboard/[search_space_id]/logs/loading.tsx
- app/dashboard/[search_space_id]/new-chat/loading.tsx
