edited company info + security check. additional fix

[gr1shan1a]

This pull request introduces several frontend and documentation updates for the concrete factory demo project, focusing on improved contact methods, delivery information, admin authentication, and clearer project setup instructions. The changes enhance usability, security, and clarity for both users and developers.

Frontend improvements:

• Added MAX messenger links to dispatcher and sales contacts in the header on both index.html and about.html, including new styling for .header-max-link in styles.css. [

• Updated delivery input to request address instead of distance, with a clarifying note about delivery pricing in index.html and corresponding CSS.

• Changed technologist info and certificate links, and added a company card link to requisites.
  Admin panel and authentication:

• Switched admin authentication to use a server-side password from environment variables, replacing the default hardcoded password. Improved error handling and messaging for login and price updates.

Documentation and configuration updates:

• Rewrote and expanded the README.md to clarify project structure, environment setup, email configuration (switching from SMTP to Resend API), admin password requirements, and GitHub Pages limitations. Provided instructions for secure password hashing and backend deployment.
• Updated company info JSON to correct spelling and added a new "Бухгалтерия" contact in concretePriceInfo.json.