🛡️ Sentinel: [CRITICAL] Fix IDOR via hardcoded encryption key

[ManupaKDU]

🚨 Severity: CRITICAL
💡 Vulnerability: Insecure Direct Object Reference (IDOR) via predictable symmetric encryption using a hardcoded universal secret key ("health") to protect URLs for sensitive patient reports in PatientReportController.
🎯 Impact: Anyone who knew the "health" key could decrypt or forge arbitrary report links and access sensitive patient data without authorization.
🔧 Fix: Upgraded SMS patient report URLs to use secure, signed HMAC-SHA256 tokens (createBillToken/decodeBillToken). This validates both the authenticity and the expiration of the token. The insecure endpoint parsing method was updated to strictly validate the new token type while allowing legacy valid links to continue functioning via a backward-compatible check. The &user= query parameter used for expiration validation was removed from new SMS links as the expiration is now securely embedded within the HMAC token itself.
✅ Verification: Ran mvn clean test to ensure no functionality is broken. Manually analyzed SecurityController implementation to ensure no compilation issues or logic bugs are introduced. Verified the new logic safely falls back for existing valid tokens.

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PR created automatically by Jules for task 15256601571448637770 started by @manupawickramasinghe

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