🛡️ Sentinel: [CRITICAL] Fix missing authentication on core API endpoints

[shadowcoder8]

🚨 Severity: CRITICAL
💡 Vulnerability: Missing authentication checks on core API endpoints allowing unauthorized access
🎯 Impact: An attacker could bypass authentication and read, modify, or delete sensitive application data
🔧 Fix: Enforced authentication via route dependencies using get_current_user
✅ Verification: Manually tested using a Python script to assert unauthenticated requests return a 401 status code

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PR created automatically by Jules for task 5103937731363151817 started by @shadowcoder8

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