Run on the nodesandbox runtime: harness toolchain, Hono server entry

The sandbox loads Vite's native tools as WASI (NAPI_RS_FORCE_WASI=error)
and only ships glue for rolldown 1.1.x. Vite 8.3 pulls rolldown 1.2.x,
whose binding needs emnapi 2.0 alpha, so boot failed with 'WASI binding
not found'. Match the runtime-host harness TanStack sample instead:

- Pin vite 8.1.3, rolldown + @rolldown/binding-wasm32-wasi 1.1.4,
  @vitejs/plugin-react 6.0.0, tailwindcss + @tailwindcss/vite 4.3.1
  (exact versions: the sandbox resolves package.json, not yarn.lock)
- Drop Nitro (it brings rolldown 1.2.x) and the Vercel config
- Hono now sits in src/server.ts, Start's server entry, routing /api/*
  ahead of start.fetch, as in the harness
- dev runs 'vite dev --host 0.0.0.0 --port 3000'; config is .mjs
- Await product recommendations in the loader to fix a hydration
  mismatch between the SSR skeleton and the settled client render

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

vercel.json

@@ -1,6 +0,0 @@
-{
-  "$schema": "https://openapi.vercel.sh/vercel.json",
-  "framework": "tanstack-start",
-  "installCommand": "corepack enable && yarn install",
-  "buildCommand": "yarn build"
-}