🛡️ Sentinel: [HIGH] Fix Server-Side Request Forgery (SSRF) in background workers

[frkr]

🚨 Severity: HIGH
💡 Vulnerability: Dynamic URLs retrieved from R2 object contents and accessed by the background worker in src/mq/MQDestiny.ts and src/mq/MQCallback.ts during fetch() calls did not have their protocol validated.
🎯 Impact: If an attacker can control the destination or callback URLs configured for background processing, they could force the worker to access arbitrary network schemes (e.g., file:, internal APIs, data URIs), resulting in a potential Server-Side Request Forgery (SSRF). Unhandled URL parsing failures would also trigger infinite background queue retry loops.
🔧 Fix: Wrapped the URL parsing in a try...catch block using new URL() and explicitly enforced that the resolved protocol must be either http: or https:. Invalid URLs now fail safely and route to an error state using MQStore rather than continually retrying. Documented this mitigation strategy in .jules/sentinel.md.
✅ Verification: Verified by running pnpm test which includes new tests validating SSRF protection in both modules.

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PR created automatically by Jules for task 13490444322795653780 started by @frkr

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