🛡️ Sentinel: [HIGH] Enforce Trusted Types for DOM XSS protection

[keough99]

🚨 Severity: HIGH
💡 Vulnerability: The static HTML pages lacked Trusted Types enforcement, which could allow DOM-based XSS attacks if an injection vulnerability is ever discovered.
🎯 Impact: Without Trusted Types, attackers who manage to inject malicious strings into DOM sinks could execute arbitrary scripts.
🔧 Fix: Added require-trusted-types-for 'script'; trusted-types 'none'; to the <meta http-equiv="Content-Security-Policy"> tags to completely block all DOM-based XSS attacks since the application does not dynamically evaluate strings or use unsafe DOM sinks.
✅ Verification: Run the automated tests (test_click_copy.py and test_skip_link.py) to verify that the strict CSP does not break any functionality.

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PR created automatically by Jules for task 15212737099801990996 started by @keough99

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