🛡️ Sentinel: [MEDIUM] Fix insecure random number generation

[n24q02m]

🚨 Severity: MEDIUM
💡 Vulnerability: The application used the cryptographically insecure Math.random() function to calculate exponential backoff jitter in network retry logic (background.js). While often sufficient for non-sensitive random distributions, relying on Math.random() establishes an insecure pattern that might be copied or expanded to sensitive areas (e.g., generating session IDs or CSRF tokens) in browser extensions.
🎯 Impact: Predictability can be exploited in certain timing or entropy-depletion attacks.
🔧 Fix: Replaced Math.random() with crypto.getRandomValues(new Uint32Array(1))[0] / 4294967296 to generate secure random floats in background.js and updated the corresponding test mocks in tests/background.test.js.
✅ Verification: Ran node --test and confirmed all background tests pass with the new mock for crypto.getRandomValues.

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PR created automatically by Jules for task 3124224403655075583 started by @n24q02m

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Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

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