feat: enhance browser error log for undefined process.env

[chenjiahan]

Summary

Add helpful guidance when users encounter process is not defined errors in the browser. The enhanced log explains how to properly use environment variables and suggests polyfill options.

Before

After

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR enhances error messaging for browser-side process is not defined errors by providing actionable guidance on how to properly use environment variables in a browser context.

• Adds intelligent error log enhancement that detects process is not defined errors and appends helpful instructions
• Includes test coverage for the new browser error enhancement functionality
• Fixes minor formatting issue in plugin hint messages

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/core/src/server/browserLogs.ts	Implements error detection and enhancement logic for process is not defined errors
packages/core/src/helpers/format.ts	Adds newline to plugin recommendation message formatting
e2e/cases/diagnostic/process-undefined/src/index.js	Adds test fixture that triggers process undefined error
e2e/cases/diagnostic/process-undefined/index.test.ts	Adds E2E test verifying enhanced error message appears

Comments suppressed due to low confidence (1)

packages/core/src/server/browserLogs.ts:1

• [nitpick] The multi-line string uses inconsistent indentation with hardcoded spaces. Consider extracting this message to a constant or using template literals with proper indentation for better maintainability.

import path from 'node:path';

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