feat: In-text citing (#175)

.changeset/olive-bulldogs-boil.md

helpers/env-variables.ts

templates/components/engines/python/chat/__init__.py

...tes/components/engines/python/chat/node_postprocessors.py

templates/types/streaming/fastapi/app/api/services/file.py

...xtjs/app/components/ui/chat/chat-message/chat-sources.tsx

...ming/nextjs/app/components/ui/chat/chat-message/index.tsx

...g/nextjs/app/components/ui/chat/chat-message/markdown.tsx

...es/types/streaming/nextjs/app/components/ui/chat/index.ts

...tes/types/streaming/nextjs/app/components/ui/lib/utils.ts