Can AI replace Admix?

Build me a local multi-model comparison chat to replace Admix. Requirements:

- Node 22 + Express + better-sqlite3, a server-rendered shell with a little vanilla
  JS for streaming; no frontend framework, no build step.
- One OpenRouter key in .env, kept server-side; the server proxies all model calls.
- A model picker fed from OpenRouter's /models endpoint; select up to four models.
- One prompt fans out to the selected models and streams each reply into a
  side-by-side grid with model name, elapsed time, and token usage when reported;
  a failed model shows its error in its own column without killing the others.
- Markdown rendering with fenced code blocks and a copy button per reply.
- Threads, prompts, model ids, replies, and timestamps in SQLite; full-text search
  across saved threads; export a thread as Markdown.
- A running cost estimate per thread from OpenRouter's usage and pricing fields.
- Binds to localhost only. No accounts, no telemetry; prompts and replies leave the
  machine only for OpenRouter, and the README says so.
- Out of scope: auth, billing, mobile apps, image generation, hosted sync, and
  provider-specific tools like web search or file upload.
- README: setup, .env.example, and how to add a model id by hand if the catalog
  fetch fails.