🛡️ Sentinel: [HIGH] Fix XSS risk by enforcing strict CSP

[AstroMyth101]

🚨 Severity: HIGH
💡 Vulnerability: The Content-Security-Policy allowed inline scripts via unsafe-inline in the script-src directive, weakening XSS protection.
🎯 Impact: Attackers could potentially execute arbitrary inline scripts if they found a way to inject them.
🔧 Fix: Extracted the inline theme script in base.njk to a separate theme-init.js file, enabling the use of script-src 'self'.
✅ Verification: Built the project and verified the <meta> tag now has the stricter CSP.

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PR created automatically by Jules for task 8399696705611433011 started by @AstroMyth101

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