feat: add production playground for testing the real user install path

[antfubot]

Description

Adds playgrounds/production: a standalone pnpm workspace that installs Vite DevTools from the local built dist, so the tools can be exercised the way a real user consumes them — from the packaged artifacts, with no monorepo aliases, src imports, or workspace: links.

Where packages/core/playground aliases everything to source for fast iteration, this playground does the opposite: it packs the published packages into tarballs and installs them, exercising the real npm install path and the shipped dist.

How it works

• scripts/pack-local.mjs builds the monorepo and runs pnpm pack on the five published packages (@vitejs/devtools, -kit, -rolldown, -vite, -vitest). pnpm pack rewrites each package's workspace:*/catalog:* protocols into concrete versions, producing exactly what npm would serve. Tarballs land in .tarballs/ under stable names.
• pnpm-workspace.yaml makes it its own workspace root (isolated from the monorepo) and uses overrides to point every @vitejs/devtools-* package at those tarballs. Everything else (devframe, @devframes/*, vite, vue) resolves from the public registry — just like a real install.
• vite.config.ts is a plain user config importing DevTools from @vitejs/devtools, plus a minimal Vue app so the panels have real build/module data.

Usage

cd playgrounds/production
pnpm run setup   # build monorepo + pack + install from tarballs
pnpm dev         # embedded DevTools panel
pnpm build       # production build

Verified locally

• Build → pack → pnpm install all succeed; @vitejs/devtools links to the local tarball, registry deps resolve normally.
• pnpm build completes with the DevTools() plugin loaded from dist.
• Dev server serves the real DevTools client at /__devtools/ (HTTP 200, <title>Vite DevTools</title>).

Linked Issues

Additional context

Generated artifacts (.tarballs/, node_modules, dist, lockfile) are gitignored.

This PR was created with the help of an agent.

[pkg-pr-new]

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@vitejs/devtools

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@vitejs/devtools-kit

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@vitejs/devtools-oxc

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@vitejs/devtools-rolldown

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@vitejs/devtools-vite

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@vitejs/devtools-vitest

npm i https://pkg.pr.new/vitejs/devtools/@vitejs/devtools-vitest@413

commit: 03012b6