Added dev-proxy.sh, dev-start.sh

[iAbhi001]

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PR Title

docs: add remote backend proxy pattern for hybrid dev environments

Description

This PR addresses #41406 by introducing a standard pattern for developing frontends locally while connecting to a remote backend (API/DB).

The current Preview MCP documentation assumes a unified local stack. However, developers often face resource constraints (RAM/CPU) or utilize shared development servers, necessitating a bridge between the local Vite dev server and a remote gateway.

Changes

• Added dev-proxy.mjs: A lightweight, zero-dependency Node.js reverse proxy using node:http.
• Added dev-start.sh: A cross-platform shell wrapper to orchestrate the lifecycle of both the proxy and Vite.
• Includes specific fixes for:
  • Node.js 24 IPv6 resolution: Forces family: 4 to prevent connection hangs.
  • macOS Compatibility: Uses POSIX-compliant wait instead of wait -n (which requires Bash 4+).
  • CORS handling: Manually injects headers to allow local development against remote origins.

Architecture

The pattern implements the following flow:
Browser → Vite (5173) → dev-proxy (5174) → Remote Gateway (8080)

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Technical Implementation Details

The Proxy (dev-proxy.mjs)

• Port: 5174
• Feature: Explicitly handles OPTIONS preflight requests and adds Access-Control-Allow-Origin headers.
• Reliability: Uses the family: 4 option in http.request to bypass known DNS resolution issues in Vite 7/Node 24 environments.

The Orchestrator (dev-start.sh)

• Uses a trap mechanism to ensure that stopping the script (Ctrl+C) kills both the proxy and Vite processes simultaneously, preventing "ghost" processes from occupying ports.
• Configurable via GATEWAY_HOST environment variable.

How to Test

1. Place dev-proxy.mjs and dev-start.sh in the scripts/ directory.
2. Set your remote IP: export GATEWAY_HOST="your.remote.ip".
3. Run ./scripts/dev-start.sh.
4. Verify that API calls from the frontend are successfully routed to the remote backend through the proxy.

Checklist

• Tested on macOS (Bash 3.2 compatibility)
• Tested on Linux
• Verified Node.js 24 compatibility
• No new dependencies added (uses native node:http)

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