feat: host local files and add viewer for PDFs (#85)

.changeset/weak-bobcats-trade.md

templates/types/streaming/express/index.ts

templates/types/streaming/fastapi/main.py

...lates/types/streaming/nextjs/app/api/data/[path]/route.ts

.../streaming/nextjs/app/components/ui/chat/chat-sources.tsx

...aming/nextjs/app/components/ui/chat/widgets/PdfDialog.tsx

...lates/types/streaming/nextjs/app/components/ui/drawer.tsx

...lates/types/streaming/nextjs/app/components/ui/lib/url.ts

templates/types/streaming/nextjs/package.json