🛡️ Sentinel: [HIGH] Fix information disclosure and timing attack vulnerabilities

[ivanleekk]

🚨 Severity: HIGH
💡 Vulnerability: The internal /tasks/daily-snapshot endpoint suffered from two security issues:

1. It used a basic string comparison (!=) to check the X-Scheduler-Secret header, which is vulnerable to timing attacks.
2. The global exception handler blindly returned raw exception strings (str(e)) in 500 HTTP responses, risking information disclosure of internal system states.
   🎯 Impact: An attacker could potentially bruteforce the scheduler secret using timing analysis. Furthermore, unexpected errors could leak database structures, stack traces, or other sensitive runtime information directly to clients.
   🔧 Fix:

• Replaced the string comparison with secrets.compare_digest() for constant-time secret validation (also ensuring we handle None values securely).
• Updated the exception handler to use logger.error("...", exc_info=True) to safely record the error internally, while returning a generic, non-descriptive error message to the client.
  ✅ Verification:
• Confirmed logic locally via code review.
• Ran backend pytest suite ensuring changes did not disrupt expected endpoint functionality.
• Ran ruff check to ensure syntax and formatting compliance.

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PR created automatically by Jules for task 7876005265443950948 started by @ivanleekk

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