🛡️ Sentinel: [HIGH] Fix hardcoded HMAC secret salt in webhook payload signing

[Pmaster-dev]

🚨 Severity: HIGH
💡 Vulnerability: Hardcoded HMAC secret salt "idsec_secret_salt" in server/routes.ts used for webhook payload signing.
🎯 Impact: Attackers reading the codebase could compute valid HMAC signatures and forge test webhook payloads.
🔧 Fix: Replaced hardcoded secret string with environment variable lookups (process.env.IDSEC_SECRET_SALT || process.env.WEBHOOK_SECRET) and added inline security comments.
✅ Verification: Verified code modifications, ran lint checks, and passed code review.

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PR created automatically by Jules for task 3227534910150307569 started by @Pmaster-dev

[google-labs-jules]

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