Installs and configures assistant-ui with the `assistant-ui` CLI (`create`, `init`, `add`, `update`, `upgrade`, `codemod`, `doctor`, `info`, `mcp`, `agent`) and picks the runtime adapter for a backend. Use for first-time install (`npx assistant-ui@latest create`, templates, `--example` scaffolds), adding to an existing Next.js app (`init`), or keeping an install current. Covers the runtime hook per backend: `useChatRuntime` (AI SDK v7), `useLangGraphRuntime`, `useStreamRuntime` (LangChain), `useAdkRuntime`, `useA2ARuntime`, `useAgUiRuntime`, `useEveAgentRuntime`, `useOpenCodeRuntime`, `useLocalRuntime`, `useExternalStoreRuntime`, `useDataStreamRuntime`, and `useAssistantTransportRuntime`, plus wiring guides for Mastra, Cloudflare Agents, Claude Managed Agents, LLM gateways, and Electron, the Expo (`--native`) and React Ink (`--ink`) scaffolds, and the hosted MCP docs server. Once a runtime exists, use elements for the styled Thread, runtime for hooks and adapters, and update for a deep migration.