Fix deprecated URL parsing in local proxy

[kitfoster]

Summary

• forward origin-form request targets directly through http-proxy
• avoid Node.js DEP0169 warnings for HTTP and WebSocket proxy traffic
• add regression assertions and a patch changeset

Testing

• pnpm checks -F @vercel/microfrontends
• pnpm dev:nextjs-app (30-second startup smoke test)
• pnpm dev:nextjs-pages (30-second startup smoke test)

[vercel]

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