feat: add multi-modal (file upload) and model selection to create-llama

packages/core/src/ChatEngine.ts

packages/create-llama/create-app.ts

packages/create-llama/index.ts

...-llama/templates/components/ui/shadcn/chat/chat-input.tsx

...ama/templates/components/ui/shadcn/chat/chat.interface.ts

...te-llama/templates/components/ui/shadcn/file-uploader.tsx

...a/templates/components/ui/shadcn/upload-image-preview.tsx

packages/create-llama/templates/index.ts

packages/create-llama/templates/types.ts

...ma/templates/types/streaming/nextjs/app/api/chat/route.ts

...es/types/streaming/nextjs/app/components/chat-section.tsx

...es/streaming/nextjs/app/components/ui/chat/chat-input.tsx

...reate-llama/templates/types/streaming/nextjs/constants.ts

...reate-llama/templates/types/streaming/nextjs/package.json