🔒 Fix potential XSS via innerHTML in demo-page.js

[tody-agent]

🎯 What: Fixed potential Cross-Site Scripting (XSS) vulnerabilities in public/js/demo-page.js where user-controlled strings (text and translation strings) were interpolated directly into innerHTML.
⚠️ Risk: Using innerHTML with unsanitized text allows unescaped HTML or script code execution if the input is malicious or contains unexpected tags. This could lead to a user session being compromised.
🛡️ Solution: Refactored vulnerable functions (runDemo, showResult, addAiMessage, addTypingMessage, replaceWithAiMessage) to use safe DOM element construction (document.createElement()) and safely setting text via textContent or document.createTextNode().

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PR created automatically by Jules for task 7625030744720191411 started by @tody-agent

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