🛡️ Sentinel: [HIGH] Fix URI-based XSS vulnerabilities in dynamic hrefs

[longestmt]

🚨 Severity: HIGH
💡 Vulnerability: Cross-Site Scripting (XSS) via javascript: URIs being injected into dynamic href attributes (ex.mediaUrl in exercises page and info.url in settings page).
🎯 Impact: An attacker who controls these URLs could execute arbitrary JavaScript in the context of the application when a user clicks the affected links.
🔧 Fix: Introduced a sanitizeUrl utility in src/utils/sanitize.js that strictly validates the URL protocol against an allowlist (http:// or https://) and applies escapeHTML. Applied this utility to all instances where dynamic URLs are interpolated into href attributes.
✅ Verification:

1. Ran node -c on modified files to verify syntax.
2. Ran pnpm build to confirm compilation.
3. Verified the code handles javascript: protocols by returning an empty string, effectively neutralizing the payload.

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PR created automatically by Jules for task 10207364139024820208 started by @longestmt

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