🛡️ Sentinel: [security improvement] Add Trusted Types to Content Security Policy

[ImChong]

🚨 Severity: ENHANCEMENT
💡 Vulnerability: The application mitigated DOM XSS by replacing .innerHTML with safer APIs like .textContent and document.createElement, but lacked browser-level enforcement.
🎯 Impact: An attacker could potentially inject malicious scripts if developers inadvertently reintroduce unsafe DOM APIs in the future.
🔧 Fix: Appended require-trusted-types-for 'script'; to the Content-Security-Policy meta tags in all HTML files. This enforces Trusted Types, forcing the browser to reject raw strings passed to execution sinks.
✅ Verification: Ran npm run check and verified the CSP updates using grep. Also documented the enhancement in .jules/sentinel.md.

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PR created automatically by Jules for task 2224841126680113195 started by @ImChong

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