🛡️ Sentinel: [MEDIUM] Add input validation to webhook update endpoint

[Pmaster-dev]

🚨 Severity: MEDIUM
💡 Vulnerability: Missing input validation on webhook update PUT /api/webhooks/:id
🎯 Impact: Updating webhooks permitted malformed or unsafe URLs (e.g. non-http/https schemes) and invalid event payload formats.
🔧 Fix: Added URL protocol validation (requiring http:// or https://) and Array type validation for events in PUT /api/webhooks/:id.
✅ Verification: Ran test suite (npm test), type check (npm run type-check), linting (npm run lint), and verified build (npm run build).

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PR created automatically by Jules for task 17193834906313075085 started by @Pmaster-dev

[google-labs-jules]

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