feat: add standardized error codes for Express errors

[gayanMatch]

Description

Implements standardized error codes for Express-thrown errors as proposed in #6951.

Changes

• Add lib/errors.js with error code constants and factory helpers
• Expose express.errorCodes (frozen object) for programmatic error handling
• Add code property to all 15 errors thrown by Express
• Use Error.captureStackTrace for clean stack traces
• Add tests for error codes

Error Codes

Code	Location
ERR_INVALID_STATUS_CODE	res.status()
ERR_STATUS_CODE_OUT_OF_RANGE	res.status()
ERR_SENDFILE_PATH_REQUIRED	res.sendFile()
ERR_SENDFILE_PATH_NOT_STRING	res.sendFile()
ERR_SENDFILE_PATH_NOT_ABSOLUTE	res.sendFile()
ERR_CONTENT_TYPE_ARRAY	res.set()
ERR_COOKIE_SECRET_REQUIRED	res.cookie()
ERR_MIDDLEWARE_REQUIRED	app.use()
ERR_ENGINE_CALLBACK_REQUIRED	app.engine()
ERR_HEADER_NAME_REQUIRED	req.get()
ERR_HEADER_NAME_NOT_STRING	req.get()
ERR_NO_DEFAULT_ENGINE	View
ERR_VIEW_ENGINE_NOT_FOUND	View
ERR_INVALID_ETAG_OPTION	app.set('etag')
ERR_INVALID_QUERY_PARSER_OPTION	app.set('query parser')

Usage

const express = require('express');
const { errorCodes } = express;

app.use((err, req, res, next) => {
  if (err.code === errorCodes.ERR_INVALID_STATUS_CODE) {
    // handle programmatically
  }
});

Closes #6951

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Contribution by Gittensor, see my contribution statistics at https://gittensor.io/miners/details?githubId=132382032