Rebuild the hub on Bun: Elysia API, Better Auth, Drizzle, Next.js website

The hub becomes a Bun monorepo: apps/api (Elysia, Better Auth for accounts, roles, bans, proxy device
sign-in and JWT keys; tagline linking, presence and the console as before), packages/db (Drizzle; Postgres in
production, PGlite in development and tests), and the Next.js website from apps/web. Self-hostable with
docker compose; the website deploys to Vercel-style hosts, the API to any that runs Bun or containers. The
first version, in Go, is removed.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/design.md

@@ -336,9 +336,13 @@ The proxy streams and adds no waiting.
 ## Status
 
 - Phase 1 (local packs) done: t5de-api, t5de-proxy `internal/products`.
-- Phase 2 (hub identity) started: accounts, tagline linking, age, link caps, device sign-in, presence and badge,
-  console. Not yet: periodic age re-checks (only on demand), a sign-in UI in the client (the proxy's `signin`
+- Phase 2 (hub identity) under way: accounts, tagline linking, age, link caps, device sign-in, presence and badge,
+  console. Not yet: periodic age re-checks (on demand only), a sign-in button in the client (the proxy's `signin`
   command for now), deployment.
+- **Stack changed** (2026-10-29, the user's choice): the hub is a Bun monorepo: Elysia API, Better Auth, Drizzle on
+  Postgres, Next.js website with Tailwind and shadcn/ui (README). It replaces the first version, in Go. Where this
+  document says Go or templ for the hub, read that; catalogs are still to be decided (a Bun program compiled to one
+  file would keep them easy to run).
 
 ## Phases