chore(studio): wire self-hosted run + e2e env handling for TanStack build

Previous setup ran the studio under `vite preview` and signalled e2e
mode via `NODE_ENV=test`. That broke twice on this branch:

1. `NODE_ENV=test` in the shell overrides Vite's default
   `NODE_ENV=production` for `vite build`, which makes
   `@vitejs/plugin-react` emit the dev JSX runtime (`jsxDEV`). The
   production SSR bundle doesn't have `jsxDEV` available, so every SSR
   request crashed with `TypeError: jsxDEV is not a function`.
2. `vite preview` is a static SPA preview; it can't reuse the
   `fetch`-handler shape that `apps/studio/api/server.js` exposes to
   Vercel. Self-hosted prod needs its own HTTP listener for the same
   handler.

Changes:

- Swap `NODE_ENV=test` for `MODE=test` end-to-end. `vite build --mode
  test` keeps `NODE_ENV=production` automatically (per Vite docs), so
  the React plugin stays on the prod JSX runtime and TanStack Start
  bakes the right `NODE_ENV` into the SSR bundle. `.env.test` overrides
  load through the standard `loadEnv(mode, ...)` order, so the
  developer's `.env.local` no longer leaks `NEXT_PUBLIC_IS_PLATFORM=true`
  into e2e builds.
- Explicitly set `NEXT_PUBLIC_IS_PLATFORM=false` in
  `generateLocalEnv.js` so `.env.test` (which loads after `.env.local`)
  wins regardless of what a developer has set locally.
- Add `apps/studio/scripts/serve.js`: a small zero-dep Node HTTP
  adapter that loads env files, serves `dist/client/*` statics with
  proper cache headers, and forwards everything else to the
  `fetch`-handler exported by `dist/server/server.js` — the same
  handler `api/server.js` hands to Vercel. `pnpm start` runs this;
  `pnpm preview` keeps the old `vite preview` flow as a debug
  escape-hatch.
- Add `dist/**` to studio's turbo outputs so cached builds restore
  the Vite output (not just the legacy `.next/**`).
- Declare `MODE`, `PORT` in turbo env so cache invalidates correctly
  when switching between test and production builds.

scripts/generateLocalEnv.js

@@ -11,7 +11,10 @@ const defaultEnv = {
   // NEXT_ANALYTICS_BACKEND_PROVIDER: 'postgres',
   // SUPABASE_REST_URL: 'http://127.0.0.1:54321/rest/v1/',
   // NEXT_PUBLIC_ENABLE_LOGS: 'false',
-  // NEXT_PUBLIC_IS_PLATFORM: 'false',
+  // E2E tests target self-hosted studio (no auth). Explicitly written so that
+  // .env.test overrides any IS_PLATFORM=true that a developer's .env.local
+  // might set for their own platform-mode work.
+  NEXT_PUBLIC_IS_PLATFORM: 'false',
   PG_META_CRYPTO_KEY: 'SAMPLE_KEY',
   POSTGRES_PASSWORD: 'postgres',
   POSTGRES_HOST: 'db',
@@ -31,7 +34,7 @@ const defaultEnv = {
   NEXT_PUBLIC_HCAPTCHA_SITE_KEY: '10000000-ffff-ffff-ffff-000000000001',
   NEXT_PUBLIC_NODE_ENV: 'test',
   SNIPPETS_MANAGEMENT_FOLDER: '../../supabase/snippets',
-  EDGE_FUNCTIONS_MANAGEMENT_FOLDER: '../../supabase/functions' // path relative to studio project
+  EDGE_FUNCTIONS_MANAGEMENT_FOLDER: '../../supabase/functions', // path relative to studio project
 }
 
 const environment = { ...generatedEnv, ...defaultEnv }