🛡️ Sentinel: [CRITICAL] Fix Command Option Injection

[dttdrv]

🚨 Severity: CRITICAL
💡 Vulnerability: The mainFile parameter in backend/src/services/compileQueue.ts was passed to the latexmk command via the Rust compile worker without validating if it looked like a flag (i.e., starting with a -).
🎯 Impact: An attacker could craft a compile job where the mainFile was a malicious flag like -shell-escape, potentially leading to remote command execution on the worker server, depending on the LaTeX distribution configuration.
🔧 Fix: Added a check to explicitly reject mainFile inputs that start with a hyphen.
✅ Verification: Validated that inputs starting with - are correctly rejected with a 400 Bad Request HttpError. Tests were run and code review was completed to verify safety.

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PR created automatically by Jules for task 1816402237701966379 started by @dttdrv

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