Fix standalone workspace-browser packaging for Playwright metadata

[tongchen92]

Source evidence

Two NotFair MCP feedback reports (nowork-studio/notfair-mcp #759 and #777) identify the same current source-repo failure: browser_open cannot launch from the packaged standalone install because Playwright cannot resolve its packaged browsers.json.

The live source owns this path:

• notfair/src/server/mcp-server/browser-tools.ts calls getOrLaunchBrowser() before opening a tab.
• notfair/package.json ships the standalone package and declares playwright-core.
• notfair/scripts/copy-standalone-assets.mjs dereferences and copies standalone package assets, but has no Playwright metadata inclusion/self-check.

Scope

Make the standalone package include the Playwright metadata required by the workspace-browser runtime, and make the startup failure actionable when that package invariant is missing. Do not change browser account/session behavior, OAuth, or navigation semantics.

Acceptance checks

• A packaged standalone artifact contains the Playwright browsers.json resolution target needed by the installed playwright-core runtime.
• A focused regression proves the packaging/self-check behavior rather than relying on a developer node_modules tree.
• browser_open reports a clear repair/package-integrity error if that invariant is absent; it must not claim the browser was launched.
• Existing browser-tool tests and TypeScript typecheck pass.

Non-goals

• No OAuth/profile-selection changes.
• No browser tool namespace change.
• No changes to external Chrome installation or customer credentials.