bug: fix flexbox layouts for mobile viewports inside MiniPay

[devmocrea]

Description

Review and refine CSS flexbox styles in apps/web/src/app/page.tsx to ensure all components scale down cleanly on small screens inside the Opera MiniPay webview.

Technical Specification

• Inspect layout using Chrome Developer Tools set to mobile viewports.
• Replace fixed widths (e.g. width: 500px) with responsive Tailwind percentages or flex layouts.
• Add horizontal padding to containers to prevent elements from clinging to screen edges.

Acceptance Criteria

• No horizontal scrolling or cropped containers appear on screens under 360px wide.