🛡️ Sentinel: [security improvement] Harden CSP and Referrer Policy

[Shin5hi]

🛡️ Sentinel: [security improvement] Harden CSP and Referrer Policy

🚨 Severity: MEDIUM (Security Enhancement / Defense in Depth)

💡 Vulnerability:
The application previously used a weak Content Security Policy (style-src 'self' 'unsafe-inline'; script-src 'self' 'unsafe-inline';) which allowed any inline scripts or styles to execute, significantly increasing the risk of Cross-Site Scripting (XSS) attacks. Additionally, the lack of a Referrer Policy could lead to leaking sensitive URL information to external sites.

🎯 Impact:
Potential for XSS exploitation if an attacker can inject content into the page. Exposure of internal URL structures via Referer headers.

🔧 Fix:

1. Harden CSP: Removed 'unsafe-inline' and whitelisted specific inline <style> and <script> blocks using SHA-256 hashes.
2. Defense in Depth: Added object-src 'none', base-uri 'self', and upgrade-insecure-requests to the CSP meta tag.
3. Privacy Protection: Added <meta name="referrer" content="no-referrer"> to prevent information leakage.

✅ Verification:

• Calculated hashes for existing inline content.
• Ran a Playwright verification script that:
  • Starts a local server.
  • Navigates to the page and monitors the console for CSP violation errors.
  • Interacts with the application (clicks the button) to ensure dynamic content and state transitions still work.
• Confirmed that no CSP violations were reported and the app's functionality remains intact.

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PR created automatically by Jules for task 8887349007009375383 started by @Shin5hi

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