🛡️ Sentinel: [HIGH] Fix command injection in browser URL handler

[rschumann]

🚨 Severity: HIGH
💡 Vulnerability: Unvalidated URL parameters passed to exec.Command in browser.OpenURL can lead to command injection or SSRF if malicious schemes (like file://) are used.
🎯 Impact: An attacker could potentially execute local files, access sensitive local resources, or manipulate the browser process through maliciously crafted URLs.
🔧 Fix: Added strong URL validation using net/url.Parse() to ensure only http and https schemes are allowed before passing the URL to any OS commands or libraries. Renamed url variable to rawurl to avoid shadowing the net/url package.
✅ Verification: Run go test ./... -short to ensure no regressions and verify go vet ./... passes.

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PR created automatically by Jules for task 6750862478014155570 started by @rschumann

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