🛡️ Sentinel: [HIGH] Fix timing attack vulnerability in token validation

[thirdeyenation]

🚨 Severity: HIGH
💡 Vulnerability: String comparison operators (== or !=) are used for validating authentication tokens, CSRF tokens, and API keys. This makes the application vulnerable to timing attacks.
🎯 Impact: An attacker can use the difference in response time to guess tokens byte by byte, potentially bypassing authentication or CSRF protection.
🔧 Fix: Implemented constant-time string comparison using secrets.compare_digest in helpers/api.py and helpers/ws.py. Added type checks to ensure only strings are compared to avoid TypeError.
✅ Verification: Tests have been verified to pass without regression.

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PR created automatically by Jules for task 9054479891520999072 started by @thirdeyenation

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