Add README and interactive demo sections to landing page; replace Lucide icons with inline SVGs

[helloroman-bez]

Motivation

• Provide a complete project brief and implementation guidelines by adding a README.md with product positioning, KPIs, design and technical requirements.
• Improve the landing page UX by adding an interactive, autoplaying demo of the product interface to better demonstrate value and increase conversion.
• Reduce runtime dependency on the external icon library by inlining SVG icons to make the page more resilient and performant.

Description

• Added README.md containing the full landing brief, design requirements, technical specs and local run instructions (including python -m http.server 8080).
• Extended index.html with new sections: a demo interface (#demo) with tabs/screens (Dashboard, Leads list, Chat), benefits (#benefits) and cases (#cases), and corresponding HTML structure and accessibility attributes.
• Replaced many data-lucide icon placeholders with inline SVG elements and kept the Lucide CDN load/fallback logic at the end of the document for backward compatibility.
• Added new CSS rules and responsive layouts for the demo, benefits and cases blocks, and added JS to enable auto-rotation of demo screens every 5 seconds with pause-on-hover/focus and keyboard/click activators (setDemoScreen, startDemoRotation, stopDemoRotation).

Testing

• No automated tests were executed as part of this change.

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Codex Task